Chemical Reactions and Equations - Class 10 Science - Chapter 1 - Notes, NCERT Solutions & Extra Questions
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Notes - Chemical Reactions and Equations | Class 10 NCERT | Science
Chemical reactions and equations form the backbone of understanding chemistry at any level, especially for Class 10 students. This guide aims to provide detailed notes on this vital topic, focusing on definitions, types, and methods of balancing chemical equations.
Introduction to Chemical Reactions and Equations
Chemical reactions are processes where substances undergo a transformation to form new substances. These changes are fundamental in both everyday life and industrial processes. Some common examples include:
Milk getting sour in room temperature
Iron rusting when exposed to moist air
Grapes fermenting to make wine
Cooking food
Digestion of food in our bodies
These examples illustrate that the nature and identity of the initial substances change, indicating a chemical reaction has taken place.
What is a Chemical Reaction?
A chemical reaction involves the breaking and making of bonds between atoms to produce new substances. It can be identified by observing:
Change in color
Evolution of gas
Change in temperature
Formation of a precipitate
Writing Chemical Equations
Writing chemical equations is an efficient way of describing chemical reactions. There are two main types of equations: word equations and chemical equations.
Word Equations
A word equation provides a detailed, long-form description of a chemical reaction. For example: $ \text{Magnesium} + \text{Oxygen} \rightarrow \text{Magnesium oxide} $
Chemical Formulas
To make equations more concise, chemical symbols are used: $ \text{Mg} + \text{O}_2 \rightarrow \text{MgO} $
Balancing Chemical Equations
Law of Conservation of Mass
Balancing chemical equations ensures that the number of atoms of each element is the same on both sides of the equation, adhering to the law of conservation of mass.
Steps to Balance Chemical Equations
Example:
$$ \text{Fe} + \text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + \text{H}_2 $$
Write the unbalanced equation: $$ \text{Fe} + \text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + \text{H}_2 $$
List the number of atoms of each element:
Fe: 1
H: 2
O: 1
Balance the atoms starting with the most complex molecule:
Balance oxygen by putting a coefficient of 4 in front of H₂O: $ 4\text{H}_2\text{O} $
Balance hydrogen: $ 4\text{H}_2 \rightarrow 8\text{H} $
Balance the irons: $ 3\text{Fe} $
Check and balance the entire equation: $ 3\text{Fe} + 4\text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + 4\text{H}_2 $
Ensure the equation is balanced.
Types of Chemical Reactions
Combination Reactions
Two or more substances combine to form a single product. For example: $ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 $
Decomposition Reactions
A single reactant breaks down into simpler substances. For example: $ \text{CaCO}_3 \xrightarrow{\text{heat}} \text{CaO} + \text{CO}_2 $
Displacement Reactions
One element displaces another from its compound. For example: $ \text{Fe} + \text{CuSO}_4 \rightarrow \text{FeSO}_4 + \text{Cu} $
Double Displacement Reactions
Exchange of ions between two reactants forms two new compounds. For example: $\text{Na}_2\text{SO}_4 + \text{BaCl}_2 \rightarrow \text{BaSO}_4 + \text{2NaCl} $
Redox Reactions
Involves transfer of electrons with one reactant oxidized and the other reduced. For example: $ \text{2Cu} + \text{O}_2 \xrightarrow{\text{heat}} \text{2CuO} $
Important Concepts in Chemical Reactions
Exothermic and Endothermic Reactions
Exothermic: Releases energy (e.g., Respiration).
Endothermic: Absorbs energy (e.g., Photosynthesis).
Corrosion
The gradual destruction of metals by chemical reactions with environmental agents.
Rancidity
Spoilage of oils/fats due to oxidation, causing bad taste and smell. Prevention includes using airtight containers and adding antioxidants.
Practice Questions
Write balanced equations for:
Hydrogen + Chlorine → Hydrogen chloride
Sodium + Water → Sodium hydroxide + Hydrogen
What is meant by the term 'redox reaction'?
Summary of Key Points
Chemical reactions change the nature and identity of the initial substances.
Equations must be balanced to adhere to the law of conservation of mass.
There are various types of chemical reactions like combination, decomposition, displacement, double displacement, and redox reactions.
Balancing equations involves equalizing the number of atoms of each element on both sides.
Enhance your understanding by solving practice questions and observing everyday chemical reactions in your surroundings.
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Extra Questions - Chemical Reactions and Equations | NCERT | Science | Class 10
For which of the following reactions, $\Delta H \neq \Delta U$?
(A) $\mathrm{H}_{2(g)} + \mathrm{I}_{2(g)} \rightarrow 2 \mathrm{HI}_{(g)}$
(B) $\mathrm{C}_{(s)} + \mathrm{O}_{2(g)} \rightarrow \mathrm{CO}_{(g)}$
(C) $\mathrm{N}_{2(g)} + 3 \mathrm{H}_{2(g)} \rightarrow 2 \mathrm{NH}_{3(g)}$
(D) $\mathrm{HCl}_{(aq)} + \mathrm{NaOH}_{(aq)} \rightarrow \mathrm{NaCl}_{(aq)} + \mathrm{H}_{2}\mathrm{O}_{(l)}$
The correct option is (C): $\mathbf{N_{2(g)} + 3 H_{2(g)} \rightarrow 2 NH_{3(g)}}$.
In reaction (C), the number of moles of reactants is not equal to the number of moles of products. Specifically, on the reactant side, we have $1\ \text{mol of } \mathrm{N}_{2(g)}$ and $3\ \text{mols of } \mathrm{H}_{2(g)}$, making a total of $4\ \text{moles}$. On the product side, there are $2\ \text{moles of } \mathrm{NH}_{3(g)}$.
Since $\mathrm{n\ (reactants)} \neq \mathrm{n\ (products)}$, $\Delta H \neq \Delta U$.
For which of the following reactions is Gay-Lussac's law not valid?
A $\mathrm{PCl}_{5}(\mathrm{g}) \rightarrow \mathrm{PCl}_{3}(\mathrm{g}) + \mathrm{Cl}_{2}(\mathrm{g})$
B $\mathrm{H}_{2}(\mathrm{g}) + \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{HCl}(\mathrm{g})$
C $2 \mathrm{SO}_{2}(\mathrm{g}) + \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{SO}_{3}(\mathrm{g})$
D $2 \mathrm{KClO}_{3}(\mathrm{s}) \rightarrow 2 \mathrm{KCl}(\mathrm{s}) + 3 \mathrm{O}_{2}(\mathrm{g})$
The correct answer is Option D:
$ 2 , \text{KClO}_{3}(\text{s}) \rightarrow 2 , \text{KCl}(\text{s}) + 3 , \text{O}_{2}(\text{g}) $
Gay-Lussac's law is only applicable for reactions where both reactants and products are in the gaseous state. Therefore, for the reaction to conform to Gay-Lussac's law, all participating substances must be gases.
In Option D, the reactants and one of the products (KClO$_3$ and KCl respectively) are in the solid state, making Gay-Lussac's law invalid for this reaction.
Two organic compounds 'A' and 'B' react with sodium metal and both produce the same gas 'X', but with sodium hydrogen carbonate only compound B reacts to give a gas 'Y'. Identify 'A', 'B', 'X' and 'Y':
A. A = Ethylene, B = Ethyl Alcohol, X = Carbon dioxide, Y = Hydrogen
B. A = Ethyl Alcohol, B = Acetic acid, X = Hydrogen, Y = Carbon dioxide
C. A = Methyl alcohol, B = Ethyl alcohol, X = Hydrogen, Y = Carbon dioxide
D. A = Acetic acid, B = Formic acid, X = Carbon dioxide, Y = Hydrogen
The correct answer is B.
Ethyl alcohol and acetic acid both react with sodium metal to produce the same gas, denoted as '$\mathrm{X}$'.
The reactions are as follows:
$$ 2 ,\text{C}_{2}\text{H}_{5}\text{OH} + 2,\text{Na} \rightarrow 2,\text{C}_{2}\text{H}_{5}\text{ONa} + \text{H}_{2}\uparrow $$
$$ 2 ,\text{CH}_{3}\text{COOH} + 2,\text{Na} \rightarrow 2,\text{CH}_{3}\text{COONa} + \text{H}_{2}\uparrow $$
From these reactions, it is clear that gas X is hydrogen ($\text{H}_{2}$).
When acetic acid (compound B) reacts with sodium hydrogen carbonate ($\text{NaHCO}_{3}$), it produces another gas, denoted as '$\mathrm{Y}$', through the following reaction:
$$ \text{CH}_{3}\text{COOH} + \text{NaHCO}_{3} \rightarrow \text{CH}_{3}\text{COONa} + \text{H}_{2}\text{O} + \text{CO}_{2}\uparrow $$
This reaction indicates that gas Y is carbon dioxide ($\text{CO}_{2}$).
Therefore, the identities are:
A = Ethyl alcohol
B = Acetic acid
X = Hydrogen
Y = Carbon dioxide
Thus, the final answer is B.
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Which of the statements about the reaction below are incorrect? $2 \mathrm{PbO}(\mathrm{s})+\mathrm{C}(\mathrm{s}) \rightarrow 2 \mathrm{~Pb}(\mathrm{~s})+\mathrm{CO}_{2}(\mathrm{~g})$
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
Let's analyze each statement given the provided reaction:
$$ 2 \mathrm{PbO}(s) + \mathrm{C}(s) \rightarrow 2 \mathrm{Pb}(s) + \mathrm{CO}_2(g) $$
(a) Lead is getting reduced.
This is a correct statement. In the reaction, lead (Pb) is in a compound where it has an oxidation state of +2 (in $ \mathrm{PbO} $). It is transformed into elemental lead ($ \mathrm{Pb} $) with an oxidation state of 0. Since the oxidation state of lead decreases, it is reduced.
(b) Carbon dioxide is getting oxidised.
This statement is incorrect. Carbon dioxide ($ \mathrm{CO}_2 $) is a product of the reaction, and since it is not changing its oxidation state in the course of the given chemical equation, it is neither being oxidised nor reduced.
(c) Carbon is getting oxidised.
This is a correct statement. Carbon starts in the elemental form with an oxidation state of 0 and ends up in carbon dioxide ($ \mathrm{CO}_2 $) with an oxidation state of +4. Since the oxidation state of carbon increases, it is being oxidised.
(d) Lead oxide is getting reduced.
This is a correct statement as it essentially restates (a) from the perspective of the compound $ \mathrm{PbO} $ rather than the element lead (Pb) itself.
Given the choices: (i) (a) and (b) - incorrect because (a) is true. (ii) (a) and (c) - incorrect because both (a) and (c) are true. (iii) (a), (b), and (c) - incorrect because (a) and (c) are true. (iv) all - incorrect because (a), (c), and (d) are true statements.
The only incorrect statement among (a), (b), (c), and (d) is (b), so there is no matching option in the given choices (i) to (iv). The question itself might be flawed because none of the options correctly identify the incorrect statement(s).
$\mathrm{Fe}_{2} \mathrm{O}_{3}+2 \mathrm{Al} \rightarrow \mathrm{Al}_{2} \mathrm{O}_{3}+2 \mathrm{Fe}$
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
The given reaction is:
$$\mathrm{Fe}{2} \mathrm{O}{3} + 2 \mathrm{Al} \rightarrow \mathrm{Al}{2} \mathrm{O}{3} + 2 \mathrm{Fe}$$
This reaction is an example of a displacement reaction, where aluminum ($Al$) displaces iron ($Fe$) from iron(III) oxide ($\text{Fe}_2\text{O}_3$) to form aluminum oxide ($\text{Al}_2\text{O}_3$) and free iron ($\text{Fe}$). Hence, the correct option is:
(d) displacement reaction.
What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
When dilute hydrochloric acid is added to iron fillings, the following reaction occurs:
$$ \text{Fe (s)} + 2\text{HCl (aq)} \rightarrow \text{FeCl}_2 (aq) + \text{H}_2 (g) $$
Here, iron (Fe) reacts with hydrochloric acid (HCl) to produce iron(II) chloride (FeCl₂) and hydrogen gas (H₂). So the correct answer is:
(a) Hydrogen gas and iron chloride are produced.
What is a balanced chemical equation? Why should chemical equations be balanced?
A balanced chemical equation is one in which the number of atoms of each element is the same on both sides of the equation. In a chemical reaction, matter is neither created nor destroyed, a principle known as the law of conservation of mass. As a result, chemical equations must be balanced to reflect this law – the total mass of the reactants must equal the total mass of the products.
Balancing a chemical equation ensures that the same number of atoms of each element is present on both the reactant and product sides. This gives the correct stoichiometry of the reaction, allowing us to:
Understand the exact ratio in which different reactants react to form products.
Calculate the amounts of reactants needed or products formed in a reaction.
Predict the outcome of the reaction under specified conditions.
Not balancing a chemical equation would imply that atoms are either disappearing or being created during the reaction, which is not possible according to the law of conservation of mass.
Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Sure, let's translate each of the given statements into chemical equations and then balance them:
(a) Hydrogen gas combines with nitrogen to form ammonia. Unbalanced chemical equation: $$ \text{N}_2(g) + \text{H}_2(g) \rightarrow \text{NH}_3(g) $$ Balanced chemical equation: $$ \text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g) $$
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide. Unbalanced chemical equation: $$ \text{H}_2\text{S}(g) + \text{O}_2(g) \rightarrow \text{H}_2\text{O}(l) + \text{SO}_2(g) $$ Balanced chemical equation: $$ 2\text{H}_2\text{S}(g) + 3\text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(l) + 2\text{SO}_2(g) $$
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate. Unbalanced chemical equation: $$ \text{BaCl}_2(aq) + \text{Al}_2(\text{SO}_4)_3(aq) \rightarrow \text{AlCl}_3(aq) + \text{BaSO}_4(s) $$ Balanced chemical equation: $$ 3\text{BaCl}_2(aq) + \text{Al}_2(\text{SO}_4)_3(aq) \rightarrow 2\text{AlCl}_3(aq) + 3\text{BaSO}_4(s) $$
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas. Unbalanced chemical equation: $$ \text{K}(s) + \text{H}_2\text{O}(l) \rightarrow \text{KOH}(aq) + \text{H}_2(g) $$ Balanced chemical equation: $$ 2\text{K}(s) + 2\text{H}_2\text{O}(l) \rightarrow 2\text{KOH}(aq) + \text{H}_2(g) $$
In each equation:
'(g)' denotes gaseous state.
'(l)' denotes liquid state.
'(aq)' denotes aqueous solution or substance dissolved in water.
'(s)' denotes solid state, including precipitates.
Balance the following chemical equations.
(a) $\mathrm{HNO}_{3}+\mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{H}_{2} \mathrm{O}$
(b) $\mathrm{NaOH}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}$
(c) $\mathrm{NaCl}+\mathrm{AgNO}_{3} \rightarrow \mathrm{AgCl}+\mathrm{NaNO}_{3}$
(d) $\mathrm{BaCl}_{2}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{BaSO}_{4}+\mathrm{HCl}$
To balance the given chemical equations, we need to ensure that the number of atoms of each element on the reactant side is equal to the number on the product side.
(a) For the reaction of nitric acid with calcium hydroxide: $$ 2\mathrm{HNO}{3}+\mathrm{Ca}(\mathrm{OH}){2} \rightarrow \mathrm{Ca}\left(\mathrm{NO}{3}\right){2}+2\mathrm{H}_{2} \mathrm{O} $$
(b) For the reaction of sodium hydroxide with sulfuric acid: $$ 2\mathrm{NaOH}+\mathrm{H}{2} \mathrm{SO}{4} \rightarrow \mathrm{Na}{2} \mathrm{SO}{4}+2\mathrm{H}_{2} \mathrm{O} $$
(c) For the reaction of sodium chloride with silver nitrate: $$ \mathrm{NaCl}+\mathrm{AgNO}{3} \rightarrow \mathrm{AgCl}+\mathrm{NaNO}{3} $$
(d) For the reaction of barium chloride with sulfuric acid: $$ \mathrm{BaCl}{2}+\mathrm{H}{2} \mathrm{SO}{4} \rightarrow \mathrm{BaSO}{4}+2\mathrm{HCl} $$
Each of these equations is now balanced with the same number of each type of atom on both sides of the reaction arrow.
Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide $\rightarrow$ Calcium carbonate + Water
(b) Zinc + Silver nitrate $\rightarrow$ Zinc nitrate + Silver
(c) Aluminium + Copper chloride $\rightarrow$ Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate $\rightarrow$ Barium sulphate + Potassium chloride
(a) The balanced chemical equation for the reaction between calcium hydroxide and carbon dioxide is: $$ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} $$
(b) The balanced chemical equation for the reaction between zinc and silver nitrate is: $$ \text{Zn} + 2\text{AgNO}_3 \rightarrow \text{Zn(NO}_3\text{)}_2 + 2\text{Ag} $$
(c) The balanced chemical equation for the reaction between aluminium and copper chloride is: $$ 2\text{Al} + 3\text{CuCl}_2 \rightarrow 2\text{AlCl}_3 + 3\text{Cu} $$
(d) The balanced chemical equation for the reaction between barium chloride and potassium sulphate is: $$ \text{BaCl}_2 + \text{K}_2\text{SO}_4 \rightarrow \text{BaSO}_4 + 2\text{KCl} $$
Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide(aq) + Barium iodide(aq) $\rightarrow$ Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) $\rightarrow$ Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) $\rightarrow$ Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) $\rightarrow$ Magnesium chloride(aq) + Hydrogen(g)
(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)Balanced equation: $$ \text{2KBr(aq)} + \text{BaI}_2\text{(aq)} \rightarrow \text{2KI(aq)} + \text{BaBr}_2\text{(s)} $$ Type of reaction: This is a double displacement reaction (also known as a metathesis reaction), as the anions and cations in the reactants switch places to form new compounds.
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)Balanced equation: $$ \text{ZnCO}_3\text{(s)} \rightarrow \text{ZnO(s)} + \text{CO}_2\text{(g)} $$ Type of reaction: This is a decomposition reaction, as the reactant breaks down into simpler products.
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)Balanced equation: $$ \text{H}_2\text{(g)} + \text{Cl}_2\text{(g)} \rightarrow \text{2HCl(g)} $$ Type of reaction: This is a combination reaction (also called synthesis reaction), as two or more elements or simple compounds combine to form a more complex compound.
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)Balanced equation: $$ \text{Mg(s)} + \text{2HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)} $$ Type of reaction: This is a single displacement reaction (also referred to as a substitution reaction), where an element reacts with a compound and takes the place of another element in that compound. This particular case is also an example of a redox reaction because it involves the transfer of electrons from magnesium to hydrogen ions in the acid.
What does one mean by exothermic and endothermic reactions? Give examples.
Exothermic reactions are chemical reactions in which heat is released along with the formation of products. Examples of exothermic reactions include:
The burning of natural gas: $$ \text{CH}{4(g)} + 2\text{O}{2(g)} \rightarrow \text{CO}_{2(g)} + 2\text{H}2\text{O}(g) $$
Respiration, which is also an exothermic process.
Endothermic reactions are those in which energy is absorbed, typically in the form of heat. An example of an endothermic reaction is the reaction that occurs when barium hydroxide is mixed with ammonium chloride in a test tube; this process absorbs heat.
Why is respiration considered an exothermic reaction? Explain
Respiration is considered an exothermic reaction because it releases energy to the surroundings usually in the form of heat. During the process of cellular respiration, glucose combines with oxygen to produce carbon dioxide and water, along with the release of a significant amount of energy. This energy is primarily used to generate adenosine triphosphate (ATP), which is the energy currency of the cell. Any excess energy not used in the production of ATP is lost as heat.
The general equation for cellular respiration is:
$$ C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy} (ATP + heat) $$
Because the energy content of the reactants (glucose and oxygen) is higher than that of the products (carbon dioxide and water), the difference in energy is released during the reaction, which is characteristic of exothermic reactions.
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Decomposition reactions are called the opposite of combination reactions because, in a decomposition reaction, a single substance decomposes to give two or more substances. This is in contrast to a combination reaction, where two or more substances combine to form a new single substance.
As requested, here are equations for both types of reactions:
Combination reaction example: $$ \text{Hydrogen gas} (\text{H}_2) + \text{Nitrogen gas} (\text{N}_2) \rightarrow \text{Ammonia} (\text{NH}_3) $$
Decomposition reaction example: $$ \text{Calcium carbonate} (\text{CaCO}_3) \rightarrow \text{Calcium oxide} (\text{CaO}) + \text{Carbon dioxide gas} (\text{CO}_2) $$
And for the decomposition reaction mentioned in point 8(b) from the NCERT book: $$ \text{Zinc carbonate} (\text{ZnCO}_3) \rightarrow \text{Zinc oxide} (\text{ZnO}) + \text{Carbon dioxide} (\text{CO}_2) $$
These equations illustrate the fundamental difference between the two types of reactions: combination reactions build more complex molecules from simpler ones, while decomposition reactions break down compounds into simpler molecules or elements.
Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Decomposition reactions are chemical reactions in which a single compound breaks down into two or more simpler substances. The energy required for these reactions can be supplied in various forms, such as heat, light, or electricity.
Here is one example for each type of energy supply:
Heat: When calcium carbonate (( CaCO_3 )) is heated, it decomposes to form calcium oxide (( CaO )) and carbon dioxide (( CO_2 )). This reaction is commonly referred to as calcination. $$ CaCO_3(s) \xrightarrow{\text{heat}} CaO(s) + CO_2(g) $$
Light: Silver chloride (( AgCl )) decomposes into silver (( Ag )) and chlorine gas (( Cl_2 )) when exposed to light, particularly ultraviolet light. This is a photo decomposition reaction. $$ 2AgCl(s) \xrightarrow{\text{light}} 2Ag(s) + Cl_2(g) $$
Electricity: When water (( H_2O )) is subjected to an electric current, a process known as electrolysis, it decomposes into hydrogen gas (( H_2 )) and oxygen gas (( O_2 )). $$ 2H_2O(l) \xrightarrow{\text{electricity}} 2H_2(g) + O_2(g) $$
Each of these reactions is an example of a decomposition reaction where energy is supplied in a different form to cause the decomposition.
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Displacement and double displacement reactions are two types of chemical reactions that involve the exchange of elements to form new products.
Displacement Reaction:
In a displacement reaction, a more reactive element displaces a less reactive element from its compound. This type of reaction often happens in aqueous solutions and typically involves metals and halogens. The general form of a displacement reaction can be represented as: $$ A + BC \rightarrow AC + B $$ where element ( A ) is more reactive than element ( B ), thus displacing ( B ) from the compound ( BC ) to form a new compound ( AC ).
Example:A classic example of a displacement reaction is the reaction between zinc and hydrochloric acid, which can be represented by the equation: $$ Zn (s) + 2HCl (aq) \rightarrow ZnCl_2 (aq) + H_2 (g) $$ In this reaction, zinc displaces hydrogen from hydrochloric acid to form zinc chloride and hydrogen gas.
Double Displacement Reaction:
In a double displacement reaction, or metathesis reaction, two compounds exchange ions to form two new compounds. Double displacement reactions usually occur in aqueous solutions where the cations of one compound combine with the anions of the other compound. The general form of a double displacement reaction can be represented as: $$ AB + CD \rightarrow AD + CB $$ where ( AB ) and ( CD ) are two compounds, and ( AD ) and ( CB ) are the products formed due to the exchange of ions.
Example:An example of a double displacement reaction is the reaction between sodium sulfate and barium chloride, which can be represented by the equation: $$ Na_2SO_4 (aq) + BaCl_2 (aq) \rightarrow BaSO_4 (s) + 2NaCl (aq) $$ In this reaction, sodium sulfate and barium chloride exchange ions to form the precipitate barium sulfate and a solution of sodium chloride.
These reactions are fundamental in chemistry and are often used to determine the reactivity series of metals or to synthesize new compounds.
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
The refining of silver from silver nitrate solution using copper metal involves a displacement reaction. In this reaction, copper displaces silver from its solution of silver nitrate. The chemical equation for the reaction is as follows:
$$ Cu(s) + 2AgNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + 2Ag(s) $$
Here, $ Cu $ is copper, $ AgNO_3 $ is silver nitrate, $ Cu(NO_3)_2 $ is copper(II) nitrate, and $ Ag $ is silver. Solid silver is deposited, and copper(II) nitrate remains in solution.
What do you mean by a precipitation reaction? Explain by giving examples.
A precipitation reaction is a type of chemical reaction in which two solutions react and an insoluble substance, called a precipitate, is formed. This precipitate is insoluble in water and often falls out of the solution as a solid. In a precipitation reaction, typically, a double displacement reaction occurs where two compounds exchange ions to form two new compounds. One of these compounds precipitates out of the solution because it is insoluble in water.
For example, when a solution of sodium sulphate $ (\text{Na}_2\text{SO}_4) $ is mixed with a solution of barium chloride $ (\text{BaCl}_2) $, a white substance, which is insoluble in water, is formed. This substance is barium sulphate $ (\text{BaSO}_4) $, a precipitate:
$$ \text{Na}_2\text{SO}_4 (aq) + \text{BaCl}_2 (aq) \rightarrow 2\text{NaCl} (aq) + \text{BaSO}_4 (s) $$
The barium sulphate is the precipitate and sodium chloride remains in solution .
Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction
Oxidation and reduction are chemical processes often defined by the gain or loss of oxygen among other definitions like the loss or gain of electrons. Here, we will focus on the definitions involving oxygen:
(a) Oxidation is the gain of oxygen by a substance. For example:
When magnesium reacts with oxygen, it forms magnesium oxide. In this reaction, magnesium gains oxygen: $$ \text{Mg} + \text{O}_2 \to \text{MgO} $$ Here, magnesium (Mg) has been oxidized to magnesium oxide (MgO).
The oxidation of sulfur to sulfur dioxide involves the gain of oxygen: $$ \text{S} + \text{O}_2 \to \text{SO}_2 $$ Sulfur (S) gains oxygen to form sulfur dioxide (SO₂).
(b) Reduction is the loss of oxygen from a substance. For example:
When copper oxide is heated with hydrogen, copper oxide loses oxygen to form copper, and water is also formed: $$ \text{CuO} + \text{H}_2 \to \text{Cu} + \text{H}_2\text{O} $$ Copper oxide (CuO) is reduced to copper (Cu).
In the extraction of iron from its ore, iron(III) oxide loses oxygen to form iron: $$ \text{Fe}_2\text{O}_3 + 3\text{CO} \to 2\text{Fe} + 3\text{CO}_2 $$ Iron(III) oxide (Fe₂O₃) is reduced to iron (Fe) during this process.
These reactions demonstrate the concept of oxidation as the gain of oxygen and reduction as the loss of oxygen.
A shiny brown coloured element ' $\mathrm{X}$ ' on heating in air becomes black in colour. Name the element ' $\mathrm{X}$ ' and the black coloured compound formed.
The element 'X' is copper, which is a shiny brown colored metal. When copper is heated in the air, it becomes coated with a black colored layer of copper(II) oxide. Thus, the black colored compound formed is copper(II) oxide (CuO) .
Why do we apply paint on iron articles?
We apply paint on iron articles to prevent them from rusting, which is a form of corrosion. Rusting is an oxidation reaction that occurs when iron comes in contact with moisture and oxygen in the air, leading to the formation of iron oxide. By applying paint, a protective coating is formed that inhibits the contact of iron with air and moisture, thus preventing rusting.
Oil and fat containing food items are flushed with nitrogen. Why?
Oil and fat-containing food items are flushed with nitrogen to prevent oxidation. When fats and oils get oxidized, they become rancid and their smell and taste change. By flushing bags of chips or similar food items with nitrogen, a gas that does not react with the food, manufacturers can prevent the food from getting oxidized and thus avoid rancidity .
Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
(a) Corrosion:
Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, or sulfide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. Corrosion often occurs in the presence of moisture, air, and other specific environmental factors. It leads to the deterioration of the metal and is commonly seen as rusting in iron and steel when they are exposed to moisture and oxygen over time.
Example of Corrosion: Iron, when exposed to damp air or water, will react with oxygen to form iron oxide, commonly known as rust. The chemical reaction can be represented as: $$ 4Fe + 3O_2 + xH_2O \rightarrow 2Fe_2O_3\cdot xH_2O $$ This hydrated iron(III) oxide forms as a reddish-brown, flaky material on the surface of iron objects, weakening them and leading to structural failures if left unchecked.
(b) Rancidity:
Rancidity refers to the spoilage of fats and oils which results in unpleasant flavors and odors. This process can be caused by the oxidation of fatty acids when they are exposed to air, light, or moisture, or by the hydrolysis of fats into free fatty acids and glycerol. Rancidity affects the quality of food and can make it unsafe for consumption.
Example of Rancidity: An example of rancidity is the spoilage of butter. When butter is left uncovered, the fat in the butter can undergo oxidative rancidity, where the oxygen in the air reacts with the fatty acids, leading to an off-flavor and a bad odor. This is why butter is typically kept in an airtight container or refrigerated to slow down the process of rancidity.
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Ask Chatterbot AIExtra Questions and Answers - Chemical Reactions and Equations | NCERT | Science | Class 10
Which of the following elements is used to kill germs in water to make it safer?
A Oxygen
B Chlorine
C Nitrogen
D Hydrogen
The correct option is B: Chlorine.
Chlorine is added in small quantities to water to make it safer for consumption. It functions as an effective disinfectant because it is harmful to living organisms, allowing it to kill germs and other microorganisms present in the water. This property makes chlorine an essential element for water purification.
How to balance equations?
To balance chemical equations effectively, follow these systematic steps:
Identify the reactants and the products in the reaction and note their chemical formulas.
Arrange the equation with reactants on the left side and products on the right side.
Count the number of atoms for each element present in both reactants and products.
Adjust the coefficients before each compound to balance the atoms of each element across both sides.
Re-check to ensure all elements are balanced.
Example
Consider the equation that needs balancing: $$ \mathrm{Mg} + \mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2 $$
Step-by-step Balancing
Count the number of atoms in reactants and products:
Reactants:
$\mathrm{Mg} = 1$ atom
$\mathrm{H} = 1$ atom
$\mathrm{Cl} = 1$ atom
Products:
$\mathrm{Mg} = 1$ atom
$\mathrm{H} = 2$ atoms
$\mathrm{Cl} = 2$ atoms
Since there is a discrepancy in the number of $\mathrm{H}$ and $\mathrm{Cl}$ atoms, the equation is not balanced.
Adjusting coefficients: Add a coefficient of 2 before $\mathrm{HCl}$ in the reactant side: $$ \mathrm{Mg} + 2\mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2 $$
Re-count the atoms:
Reactants:
$\mathrm{Mg} = 1$ atom
$\mathrm{H} = 2$ atoms
$\mathrm{Cl} = 2$ atoms
Products:
$\mathrm{Mg} = 1$ atom
$\mathrm{H} = 2$ atoms
$\mathrm{Cl} = 2$ atoms
Conclusion
The elements are now balanced on both sides. The final balanced equation is: $$ \mathrm{Mg} + 2\mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2 $$
This systematic approach ensures that the law of conservation of mass is satisfied, where the mass of reactants equals the mass of products.
The scientist who first carried out a critical nuclear fission reaction is:
A) Otto Hahn
B) Enrico Fermi
C) Hans Bethe
D) Einstein
The correct answer is Option B: Enrico Fermi. Enrico Fermi was key in carrying out the first critical nuclear fission reaction. This achievement is pivotal in the history of nuclear physics, showcasing how nuclear energy could be harnessed.
Statement 1: Evaporation causes cooling of the liquid. Statement 2: During evaporation, the surface molecules with high kinetic energy get evaporated.
(A) Statement 1 and Statement 2 are both correct, and Statement 2 is the correct explanation of Statement 1.
(B) Statement 1 and Statement 2 are both correct, and Statement 2 is not the correct explanation of Statement 1.
(C) Statement 1 is correct, and Statement 2 is wrong.
(D) Statement 2 is correct, and Statement 1 is wrong.
The correct answer is (A) Statement 1 and Statement 2 are both correct, and Statement 2 is the correct explanation of Statement 1.
To understand this, consider the phenomena associated with evaporation. When a liquid is exposed to an environment (like in an open container), the molecules within the liquid are in constant motion, each possessing varying velocities and thus different kinetic energies. Evaporation occurs when the molecules at the surface of the liquid, particularly those with high kinetic energy, are vigorous enough to break free from the attraction forces of neighboring molecules and escape into the air above the liquid surface.
Evaporation is inherently a spontaneous process, meaning it can occur at any temperature. A key observation during evaporation is that the molecules which escape have higher kinetic energy. As a result, the average kinetic energy of the remaining molecules decreases. Given that temperature in terms of molecular motion is a measure of the average kinetic energy, the liquid’s temperature drops, which in turn explains the cooling effect.
Thus, Statement 1: "Evaporation causes cooling of the liquid," is correct because the liquid's temperature decreases due to loss of high-energy molecules. Furthermore, Statement 2: "During evaporation, the surface molecules with high kinetic energy get evaporated," is correct and also directly explains why the cooling takes place as outlined in Statement 1. Therefore, Statement 2 not only supports Statement 1 but provides the exact cause of the observed cooling effect.
Gaseous reaction in a closed vessel is reversible or irreversible. Also give an example.
Reversible Reactions
Gaseous reactions in a closed vessel are generally reversible.
Example:Consider the reaction between hydrogen gas (H₂) and iodine vapor (I₂) in a closed vessel at approximately $444^\circ C$ (717 Kelvin). When allowed to react for about 2-3 hours, hydrogen iodide (HI) gas is formed: $$ \mathbf{H}{2(\text{g})} + \mathbf{I}{2(\text{g})} \leftrightharpoons 2\mathbf{HI}_{(\text{g})} $$
In this scenario, not all the hydrogen and iodine react completely; some remains unreacted.
If we then take the formed hydrogen iodide (HI) and maintain it in the same conditions (closed vessel at 717 K), it decomposes back into hydrogen and iodine gas: $$ 2 \mathbf{HI}{(\text{g})} \leftrightharpoons \mathbf{H}{2(\text{g})} + \mathbf{I}_{2(\text{g})} $$
Again, some hydrogen iodide remains unreacted.
This behavior, where the products can revert back to the original reactants upon the same environmental conditions, signifies a reversible reaction.
A gas 'X' reacts with lime water and forms a compound 'Y' which is used as a bleaching agent in the chemical industry. Identify X and Y. Give the chemical equation of the reactions involved.
The gas 'X' is chlorine ($\text{Cl}_2$). It reacts with lime water to form a compound 'Y' known as calcium oxychloride ($\text{Ca}(\text{OCl}_2$), commonly referred to as bleaching powder. The chemical equation for the reaction is:
$$ 2 \text{Ca(OH)}_2 + 2 \text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{CaCl}_2 + 2 \text{H}_2\text{O} $$
where:
$\text{Ca(OH)}_2$ is lime water,
$\text{Cl}_2$ is chlorine,
$\text{Ca(OCl)}_2$ is calcium oxychloride (bleaching powder),
$\text{CaCl}_2$ is calcium chloride,
$\text{H}_2\text{O}$ is water.
In summary:
'X' = $\text{Cl}_2$ (chlorine)
'Y' = $\text{Ca(OCl)}_2$ (calcium oxychloride, or bleaching powder)
This reaction is significant for producing a bleaching agent used extensively in the chemical industry.
In a closed system, no change in can occur.
A. Energy
B. Pressure
C. Mass
D. Temperature
The correct answer is C. Mass.
In a closed system, there is no exchange of matter with the surroundings; hence, the mass remains constant.
What are chemical reactions?
A chemical reaction is a process where one set of chemical substances is transformed into another set. Typically, these reactions involve changes in the positions of electrons, leading to the formation and breaking of chemical bonds among atoms, without altering the nuclei (thereby the elements remain the same). These transformations can be represented via a chemical equation.
Nuclear chemistry, a specialized area of chemistry, deals with the reactions of unstable and radioactive elements where changes occur in both electron configuration and nuclear configuration.
The initial substances in a chemical reaction are referred to as reactants or reagents. Chemical reactions typically result in a chemical change, producing one or more products with properties distinct from the reactants. These reactions might unfold through a series of steps known as elementary reactions, and detailed pathways of these steps are described by the reaction mechanism.
Chemical reactions occur at a specific reaction rate, which depends on the temperature and concentration of the reactants. Generally, higher temperatures increase the reaction rate by providing more thermal energy necessary to reach the activation energy for bond breaking.
Reactions can progress in both forward and reverse directions, achieving completion or reaching a state of equilibrium. Reactions moving spontaneously toward equilibrium are termed spontaneous, and they do not require external energy to proceed. Conversely, non-spontaneous reactions need an external energy source, such as electrical energy for charging a battery or sunlight for photosynthesis.
In chemical synthesis, various chemical reactions are employed in combinations to obtain desired products. In biochemistry, sequences of chemical reactions create metabolic pathways, often catalyzed by enzymes, which are proteins that enhance reaction rates. Enzymes allow biochemical reactions to occur efficiently at the normal conditions within a cell.
Finally, the concept of a chemical reaction has been broadened to include interactions between smaller entities, such as in nuclear reactions, radioactive decay, and reactions among elementary particles as governed by quantum field theory.
What is the shorthand representation of a chemical change?
A Chemical compounds
B Chemical equation
C Chemical formula
D Chemical symbols
The correct answer is B) Chemical equation.
A chemical equation acts as a shorthand notation to represent a chemical change. It effectively illustrates the conversion of reactants to products, where each is symbolized by their respective chemical formulas. This concise notation highlights the transformation occurring during a chemical reaction.
Rashi was performing an experiment. She mixed a compound X with water in a beaker. She found that the beaker was becoming hot, releasing heat, and forming a new substance Y. She was shocked and left the room, leaving the product. After three to four days, when she returned, she found that the substance Y had changed into a shiny substance Z. What are X, Y, and Z?
(A) X, Y, Z are CaCO3, Ca(OH)2, CaO respectively. (B) X, Y, Z are Pb(NO3)2, PbO, PbCO3 respectively. (C) X, Y, Z are FeO, Fe(OH)3, FeCO3 respectively. (D) X, Y, Z are CaO, Ca(OH)2, CaCO3 respectively.
Solution:The correct option is (D).
When calcium oxide (CaO), which is substance X, is mixed with water, it reacts exothermically (releasing heat) to form calcium hydroxide (Ca(OH)₂), which is substance Y. This reaction is known as:
$$ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 $$
Over the course of a few days, calcium hydroxide left exposed to air undergoes a chemical change due to the carbon dioxide ($\text{CO}_2$) present in the atmosphere. It reacts to form calcium carbonate (CaCO₃), labeled as substance Z. This reaction can be expressed as:
$$ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} $$
This transformation results in the formation of a shiny, solid substance, which is the calcium carbonate with its characteristic shiny finish. Hence, substances X, Y, and Z correspond to CaO, Ca(OH)₂, and CaCO₃, respectively, according to option (D).
A compound '$\mathrm{X}$' of sodium is commonly used in the kitchen for making crispy fried snacks. It is also used to relieve acidity in the stomach. Identify this '$X$'. Write its chemical formula and the reactions taking place at the time of heating this compound.
The compound 'X,' commonly used in the kitchen for making crispy fried snacks and as an antacid, is baking soda. Chemically, this compound is sodium hydrogen carbonate, and its formula is given by $$ \mathrm{NaHCO}_3 $$.
When baking soda is heated, it decomposes through the following chemical reaction: $$ 2 \mathrm{NaHCO}_3 \rightarrow \mathrm{Na}_2 \mathrm{CO}_3 (\mathrm{s}) + \mathrm{H}_2 \mathrm{O}(\mathrm{l}) + \mathrm{CO}_2 (\mathrm{g}) $$
Here, $\mathrm{Na}_2 \mathrm{CO}_3$ represents sodium carbonate in solid form, $\mathrm{H}_2 \mathrm{O}$ is water in liquid form, and $\mathrm{CO}_2$ is carbon dioxide gas, which is released during the heating process.
The sum total of all the reactions taking place in a cell is called reactions.
A. Anabolic
B. Catabolic
C. Amphibolic
D. Metabolic
The correct answer is D. Metabolic.
Metabolism refers to all the reactions occurring in a cell or an organism. These reactions can be classified into two main categories: anabolic (synthetic) reactions, where molecules are constructed using energy, and catabolic reactions, where molecules are broken down, releasing energy. These two types of reactions work collectively to maintain the organism's life functions.
Write the balanced chemical equation for the following reaction: Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
For a balanced chemical equation, the number of atoms for each element in the reactants must equal the number of atoms in the products. The reaction between calcium hydroxide and carbon dioxide producing calcium carbonate and water can be represented by the following balanced equation:
$$ \mathrm{Ca(OH)_2} + \mathrm{CO_2} \rightarrow \mathrm{CaCO_3} + \mathrm{H_2O} $$
In this equation, each element (Ca, O, H, and C) has an equal number of atoms on both the reactant and product sides, ensuring the equation is balanced.
(a) What do you understand by exothermic and endothermic reactions?
(b) Give one example of an exothermic reaction and one of an endothermic reaction.
(c) Which of the following are endothermic reactions and which are exothermic reactions?
(i) Burning of natural gas
(ii) Photosynthesis
(iii) Electrolysis of water
(iv) Respiration
(v) Decomposition of calcium carbonate
(a) In exothermic reactions, heat is released along with the products, making the surroundings warmer. Conversely, endothermic reactions absorb energy from their surroundings, typically making them cooler.
(b)
Example of an exothermic reaction: Combustion of methane: $$ \text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(g) $$ This reaction releases a significant amount of heat and energy.
Example of an endothermic reaction: Dissolution of ammonium chloride in water: $$ \text{NH}_4\text{Cl}(s) \rightarrow \text{NH}_4^+(aq) + \text{Cl}^-(aq) $$ During this process, the test tube containing the mixture becomes cold, indicating heat absorption.
(c) Classification of the given reactions:
(i) Burning of natural gas: Exothermic because it involves the release of heat.
(ii) Photosynthesis: Endothermic because it requires energy in the form of sunlight.
(iii) Electrolysis of water: Endothermic because it requires electrical energy to proceed.
(iv) Respiration: Exothermic as it releases energy useful to organisms.
(v) Decomposition of calcium carbonate: $$ \text{CaCO}_3(s) \rightarrow \text{CaO}(s) + \text{CO}_2(g) $$ This process is endothermic as it requires heat to proceed.
Which of the following is an example of a double displacement reaction?
i) $\mathrm{CO}_{2}(\mathrm{g}) + \mathrm{H}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}(\mathrm{g}) + \mathrm{H}_{2}\mathrm{O}(\mathrm{g})$
ii) $\mathrm{P}_{4}\mathrm{O}_{10}$(s) $+ 6 \mathrm{H}_{2}\mathrm{O}(\mathrm{I}) \rightarrow 4 \mathrm{H}_{3}\mathrm{PO}_{4}$(aq)
iii) $\mathrm{H}_{2} + \mathrm{O}_{2} \rightarrow \mathrm{H}_{2}\mathrm{O}$
iv) $\mathrm{CoCl}_{2}(\mathrm{aq}) + \mathrm{Na}_{2}\mathrm{CO}_{3}(\mathrm{aq}) \rightarrow \mathrm{CoCO}_{3}(\mathrm{aq}) + 2\mathrm{NaCl}(\mathrm{aq})$
A) (i)
B) (ii)
C) (iii)
D) (iv)
The correct answer is D) (iv).
In a double displacement reaction, the cations and anions of two reacting compounds exchange places, resulting in the formation of two new products.
Looking at the given reactions, the formula: $$ \mathrm{CoCl}_{2}(\mathrm{aq}) + \mathrm{Na}_{2}\mathrm{CO}_{3}(\mathrm{aq}) \rightarrow \mathrm{CoCO}_{3}(\mathrm{aq}) + 2\mathrm{NaCl}(\mathrm{aq}) $$ demonstrates this behavior.
Here, the cation $\mathrm{Co}^{2+}$ from $\mathrm{CoCl}_2$ pairs with the anion $\mathrm{CO}_3^{2-}$ from $\mathrm{Na}_2\mathrm{CO}_3$, and the cation $\mathrm{Na}^+$ from $\mathrm{Na}_2\mathrm{CO}_3$ pairs with the anion $\mathrm{Cl}^-$ from $\mathrm{CoCl}_2$. This switch results in the formation of $\mathrm{CoCO}_3$ and $\mathrm{NaCl}$, illustrating a classic example of a double displacement reaction.
Which of the following reactions is exothermic?
A Sunlight: $2 \mathrm{AgNO}_{3} \rightarrow 2 \mathrm{Ag} + 2 \mathrm{NO}_{2} + \mathrm{O}_{2}$
B $\mathrm{C} + 2\mathrm{S} + \Delta \rightarrow \mathrm{CS}_{2}$
C Electric current: $2 \mathrm{NaCl} \rightarrow 2 \mathrm{Na} + \mathrm{Cl}_{2}$
D $\mathrm{C} + \mathrm{O}_{2} \rightarrow \mathrm{CO}_{2} + \Delta$
The correct answer is D.
The key aspect here is identifying which of the reactions is exothermic, meaning the reaction releases energy, usually in the form of heat.
Reaction A involves the breakdown of silver nitrate ($ \mathrm{AgNO}_3 $) under sunlight, which is generally an endothermic process as it likely requires energy from light to proceed.
Reaction B indicates the formation of carbon disulfide ($ \mathrm{CS}_2 $) from carbon and sulfur, where the "$ \Delta $" symbol suggests the need for heat, indicating it's an endothermic reaction.
Reaction C involves the electrolysis of sodium chloride ($ \mathrm{NaCl} $) using electric current, which again is an energy-consuming process, thus endothermic.
Reaction D involves the burning of carbon in the presence of oxygen to form carbon dioxide ($ \mathrm{CO}_2 $), with the "$ \Delta $" at the end signifying the release of energy, making it an exothermic reaction.
Therefore, Reaction D is the correct exothermic reaction as it involves the release of energy to the surroundings.
On passing excess CO2 through limewater, it first turns milky and then becomes colorless. Also, write the chemical equations.
When excess carbon dioxide (CO2) is passed through limewater (a solution of calcium hydroxide, [Ca(OH)2]), an interesting sequence of chemical reactions occurs. Initially, the reaction between Ca(OH)2 and CO2 produces calcium carbonate (CaCO3), a white, insoluble solid that causes the solution to turn milky due to its precipitation. The chemical equation for this reaction is: $$ \text{Ca(OH)}_2 (aq) + \text{CO}_2 (g) \rightarrow \text{CaCO}_3 (s) ↓ + \text{H}_2\text{O} (l) $$
As excess CO2 continues to be added, it further reacts with the precipitated calcium carbonate and water to form calcium bicarbonate [Ca(HCO3)2], which is soluble in water. This makes the solution turn colorless, as the precipitate dissolves back into the solution. The equation for this subsequent reaction is: $$ \text{CaCO}_3 (s) + \text{CO}_2 (g) + \text{H}_2\text{O} (l) \rightarrow \text{Ca(HCO}_3)_2 (aq) $$
Thus, the initial milkiness caused by calcium carbonate formation is cleared by the formation of the soluble calcium bicarbonate.
The balanced chemical equation for the reaction of zinc metal with hydrochloric acid is:
(A) $\mathrm{Zn}+\mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2}$
(B) $\mathrm{Zn}+\mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2}$
(C) $\mathrm{Zn}+2 \mathrm{HCl} \rightarrow 2 \mathrm{ZnCl}_{2}+\mathrm{H}_{2}$
(D) $\mathrm{Zn}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2}$
Correct Answer: D
The balanced chemical equation for the reaction between zinc metal and hydrochloric acid is:
$$ \mathrm{Zn} + 2\mathrm{HCl} \rightarrow \mathrm{ZnCl}_2 + \mathrm{H}_2 $$
In this equation, the stoichiometry is correct as the number of atoms of each element is balanced on both sides:
Zinc (Zn) is balanced with one atom on each side.
Chlorine (Cl) has two atoms on the reactant side (2 from $2\mathrm{HCl}$) and two atoms on the product side (2 from $\mathrm{ZnCl}_2$).
Hydrogen (H) has two atoms on the reactant side (2 from $2\mathrm{HCl}$) and two atoms in the hydrogen gas molecule ($\mathrm{H}_2$) on the product side.
Thus, option (D) is the accurate balanced chemical equation for this reaction.
Consider the following reaction.
$$ \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2} \rightarrow \mathrm{CuO} + \mathrm{NO}_{2} + \mathrm{O}_{2} $$
Which of the following are correct?
A) Mass of products = mass of reactants
B) Number of atoms on either side of the reaction are equal
C) Mass of reactants is not equal to mass of products
D) Number of atoms on product side is more than the reactant side
The correct answer is C) Mass of reactants is not equal to mass of products.
The reaction in question is:
$$ \mathrm{Cu}(\mathrm{NO}_{3})_{2} \rightarrow \mathrm{CuO} + \mathrm{NO}_{2} + \mathrm{O}_{2} $$
Counting the total number of atoms on each side of the equation:
Reactant side: Copper (Cu) has 1 atom, Nitrogen (N) has 2 atoms, Oxygen (O) has 6 atoms (from two $\mathrm{NO}_3$ groups).
Product side: Copper (Cu) has 1 atom in $\mathrm{CuO}$, Nitrogen (N) has 1 atom in $\mathrm{NO}_2$, and Oxygen (O) has 4 atoms in total (2 in $\mathrm{CuO}$, 1 in $\mathrm{NO}_2$, and 1 in $\mathrm{O}_2$).
It's clear that the number of atoms of oxygen differs between the reactant and product sides. Consequently, mass conservation is not observed based on the molecular weights of different elements and their stoichiometric ratios in the equation. Hence, the mass of the reactants does not equal the mass of the products, making option C correct.
What is a displacement reaction?
A displacement reaction is a type of chemical reaction where a more reactive element displaces a less reactive element from its compound. This process showcases the reactivity series of elements, demonstrating that some elements can replace others that are less effective at forming or maintaining chemical bonds in specific compounds.
Which among the following is written on the right side of a chemical equation?
A) Reactant
B) Product
C) Heat released
D) Catalyst
The right answer is B) Product.
In a chemical reaction, the products are the substances formed as a result of the reaction and are always written on the right side of the chemical equation. The reactants, on the other hand, appear on the left side.
In the reaction, $\mathrm{As}_{2} \mathrm{S}_{3} + \mathrm{xNO}_{3}^{-} + \mathrm{yH}^{+} \rightarrow 2 \mathrm{AsSO}_{4} + \mathrm{zNO}_{2} + \mathrm{aS} + 2 \mathrm{H}_{2} \mathrm{O}$.
Find the coefficients $x$, $y$, $z$, and $a$ respectively:
A $10, 4, 10, 3$ B $5, 4, 5, 3$ C $4, 10, 3, 10$ D None of these
The correct option is $\mathbf{A}$: $10, 4, 10, 3$
This reaction is a special case of a redox reaction. Specifically, it involves two oxidation reactions and one reduction reaction.
Oxidation Half-Reactions:
For Arsenic:$$ \text{As}^{3+} \rightarrow \text{AsO}_{4}^{3-} $$
For Sulfur:$$ \text{S}^{2-} \rightarrow \text{S} $$
Let's balance these two oxidation half-reactions first: 1. $$ 2 \text{As}^{3+} + 8 \text{H}_2\text{O} \rightarrow 2 \text{AsO}_{4}^{3-} + 16 \text{H}^{+} + 4 \text{e}^{-} $$ 2. $$ 3 \text{S}^{2-} \rightarrow 3 \text{S} + 6 \text{e}^{-} $$
Adding these two half-reactions: $$ 2 \text{As}^{3+} + 3 \text{S}^{2-} + 8 \text{H}_2\text{O} \rightarrow 2 \text{AsO}_{4}^{3-} + 3 \text{S} + 16 \text{H}^{+} + 10 \text{e}^{-} $$
Reduction Half-Reaction:
For Nitrate:$$ \text{NO}_{3}^{-} \rightarrow \text{NO}_{2} $$
Balancing the reduction half-reaction: $$ \text{NO}_{3}^{-} + 2 \text{H}^{+} + 1 \text{e}^{-} \rightarrow \text{NO}_{2} + \text{H}_2\text{O} $$
Combining the Reactions:
To combine the reactions, multiply the reduction half-reaction by 10 to equal the number of electrons in the oxidation half-reactions. Then, add: $$ \text{As}_2\text{S}3 + 10 \text{NO}{3}^{-} + 4 \text{H}^{+} \rightarrow 2 \text{AsO}_{4}^{3-} + 10 \text{NO}_{2} + 3 \text{S} + 2 \text{H}_2\text{O} $$
Thus, the coefficients are $x = 10$, $y = 4$, $z = 10$, and $a = 3$, matching option A.
Write balanced chemical equations for the following reactions:
(a) Hydrochloric acid reacts with calcium hydroxide: $$ \text{HCl} + \text{Ca(OH)2} \rightarrow \text{CaCl2} + \text{H2O} $$
(b) Calcium hydroxide reacts with sulphuric acid: $$ \text{Ca(OH)2} + \text{H2SO4} \rightarrow \text{CaSO4} + 2\text{H2O} $$
The equations provided are already balanced, so no further adjustments are needed. However, here’s a step-by-step guide to balance a chemical equation:
Write down the given equation.
Count the number of atoms of each element on both sides of the equation.
Balance the atoms of each element on both sides of the reaction.
Always leave hydrogen and oxygen for last to balance.
Balance the hydrogen atoms next, followed by the oxygen atoms.
Balanced Equations:
Hydrochloric acid reacts with calcium hydroxide: $$ \text{Ca(OH)}_2 (s) + 2\text{HCl} (aq) \rightarrow \text{CaCl}_2 (aq) + 2\text{H}_2\text{O} (l) $$
Calcium hydroxide reacts with sulphuric acid: $$ \text{Ca(OH)}_2 (aq) + \text{H}_2\text{SO}_4 (aq) \rightarrow \text{CaSO}_4 (s) + 2\text{H}_2\text{O} (l) $$
These steps ensure the equations are balanced for all the atoms involved while complying with the law of conservation of mass.
Consider the following substances: $\mathrm{NaCl}, \mathrm{Ca}(\mathrm{OH})_{2}, \mathrm{NaHCO}{3}, \mathrm{NH}_{3}, \mathrm{Na}{2} \mathrm{CO}_{3}, \mathrm{H}{2} \mathrm{O}, \mathrm{Cl}_{2} \mathrm{CO}{2}, \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}{2} \mathrm{O}, 2 \mathrm{CaSO}_{4} \cdot \mathrm{H}{2} \mathrm{O}$
(a) Which two substances combine to form bleaching powder?
(b) Which four substances are utilized in the production of washing soda?
(c) Which compound represents plaster of Paris?
(d) Which compound is a part of baking powder?
(e) Which compound is used as an antacid?
$\mathrm{Ca}(\mathrm{OH})_{2}$ and $\mathrm{Cl}_{2}$
$\mathrm{NaCl}, \mathrm{NH}_{3}, \mathrm{H}_{2} \mathrm{O}$ and $\mathrm{CO}_{2}$
$2 \mathrm{CaSO}_{4} \cdot \mathrm{H}_{2} \mathrm{O}$
$\mathrm{NaHCO}_{3}$
$\mathrm{NaHCO}_{3}$
In 1 g of a metal oxide, the amount of metal present is 0.68 g.
What is the equivalent weight of the metal?
A. 17 g
B. 34 g
C. 68 g
D. 52 g
The correct option is A. 17 g.
Given:
Mass of the metallic oxide: $ 1 \text{ g} $
Mass of the metal: $ 0.68 \text{ g} $
To find the mass of oxygen in the oxide:
$$ \text{Mass of oxygen} = \text{Mass of oxide} - \text{Mass of metal} $$
Substitute the given values:
$$ \text{Mass of oxygen} = 1 \text{ g} - 0.68 \text{ g} = 0.32 \text{ g} $$
Using the oxygen displacement method:
$$ \text{Equivalent weight of metal} = \left( \frac{\text{Weight of metal}}{\text{Weight of oxygen}} \right) \times \text{Equivalent weight of oxygen} $$
We know that the equivalent weight of oxygen is 8:
$$ \text{Equivalent weight of metal} = \left( \frac{0.68}{0.32} \right) \times 8 = 17 \text{ g} $$
Thus, the equivalent weight of the metal is $ 17 \text{ g} $.
Chemical equation is balanced according to the law of -
Option 1) Multiple proportion Option 2) Reciprocal proportion Option 3) Conservation of mass Option 4) Definite proportion
The correct option is C) Conservation of mass
Chemical equations are balanced to adhere to the law of conservation of mass. This law states that mass is neither created nor destroyed in a chemical reaction. Therefore, the amount of matter on the reactants' side must be equal to the amount on the products' side.
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