Chemical Reactions and Equations

Decomposition Reactions

Displacement and Double Displacement Reactions

Precipitation Reactions

Oxidation and Reduction

Chemical Equation Balancing

Types of Chemical Reactions

Corrosion and Rancidity

Exothermic and Endothermic Reactions

Chemical Reaction Indicators

Chemical Reaction Safety

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CBSE Learning Objectives – Key Concepts & Skills You Must Know

Learning Objectives

Understand decomposition reactions where energy is supplied in the form of heat, light, or electricity, and write equations for these reactions.
Differentiate between displacement and double displacement reactions and write equations for these reactions.
Define precipitation reactions and explain them with examples.
Explain oxidation and reduction in terms of gain or loss of oxygen with examples.
Learn how to balance chemical equations and understand the importance of balancing in accordance with the law of conservation of mass.
Understand different types of chemical reactions including combination, decomposition, displacement, double displacement, exothermic, and endothermic reactions.
Explain the concepts of corrosion and rancidity with examples.
Define exothermic and endothermic reactions and provide examples.
Identify indicators of chemical reactions such as color change, gas production, and temperature change.
Understand safety precautions and procedures during chemical reactions, such as handling chemicals and using equipment safely.

CBSE Revision Notes & Quick Summary for Last-Minute Study

Chapter Notes

Decomposition Reactions

Definition: Decomposition reactions involve breaking down a single compound into two or more simpler substances. These reactions require energy input in the form of heat, light, or electricity.
Examples:
- Heat: $\text{CaCO}_3 \xrightarrow{\Delta} \text{CaO} + \text{CO}_2$
- Light: $2\text{AgCl} \xrightarrow{\text{sunlight}} 2\text{Ag} + \text{Cl}_2$
- Electricity: $2\text{H}_2\text{O} \xrightarrow{\text{electricity}} 2\text{H}_2 + \text{O}_2$

Displacement and Double Displacement Reactions

Displacement Reaction: An element displaces another element from its compound.
- Example: $\text{CuSO}_4 + \text{Fe} \rightarrow \text{FeSO}_4 + \text{Cu}$
Double Displacement Reaction: Exchange of ions between two compounds.
- Example: $\text{BaCl}_2 + \text{Na}_2\text{SO}_4 \rightarrow \text{BaSO}_4 + 2\text{NaCl}$

Precipitation Reactions

Definition: Reactions that result in the formation of an insoluble product (precipitate).
Example: $\text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} \downarrow + \text{NaNO}_3$

Oxidation and Reduction

Oxidation: Gain of oxygen or loss of hydrogen.
- Example: $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$
Reduction: Loss of oxygen or gain of hydrogen.
- Example: $\text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O}$

Chemical Equation Balancing

Importance: Balancing ensures the law of conservation of mass is followed.
Steps:
1. Write the unbalanced equation.
2. Count atoms of each element.
3. Use coefficients to balance the equation.
4. Check the balance.
5. Include state symbols.

Types of Chemical Reactions

Combination Reaction: Two or more substances combine to form a single product.
Decomposition Reaction: A single compound breaks down into two or more substances.
Displacement Reaction: An element displaces another in a compound.
Double Displacement Reaction: Exchange of ions between two compounds.
Exothermic Reaction: Releases heat.
Endothermic Reaction: Absorbs heat.

Corrosion and Rancidity

Corrosion: Gradual destruction of metals by chemical reactions with the environment.
- Example: Rusting of iron.
Rancidity: Spoilage of food containing fats and oils due to oxidation.
- Prevention: Flushing with nitrogen.

Exothermic and Endothermic Reactions

Exothermic: Release of energy in the form of heat.
- Example: Combustion of methane.
Endothermic: Absorption of energy.
- Example: Photosynthesis.

Chemical Reaction Indicators

Indicators: Color change, gas production, temperature change.

Chemical Reaction Safety

Precautions: Use protective gear, handle chemicals carefully, follow proper procedures.

CBSE Exam Tips, Important Questions & Common Mistakes to Avoid

Common Mistakes & Exam Tips

Decomposition Reactions

Mistake: Students often confuse the energy source required for decomposition reactions.
- Tip: Remember that decomposition reactions can require heat, light, or electricity. Practice writing equations for each type, such as thermal decomposition of calcium carbonate.

Displacement and Double Displacement Reactions

Mistake: Confusing displacement with double displacement reactions.
- Tip: In displacement reactions, one element replaces another in a compound (e.g., Zn + CuSO₄ → ZnSO₄ + Cu). In double displacement, ions are exchanged between two compounds (e.g., NaCl + AgNO₃ → AgCl + NaNO₃).

Precipitation Reactions

Mistake: Not identifying the formation of an insoluble product.
- Tip: Precipitation reactions result in an insoluble salt. Practice identifying these reactions by writing equations like BaCl₂ + Na₂SO₄ → BaSO₄ (precipitate) + 2NaCl.

Oxidation and Reduction

Mistake: Misunderstanding oxidation and reduction in terms of oxygen.
- Tip: Oxidation involves gain of oxygen, while reduction involves loss of oxygen. Use examples like 2Mg + O₂ → 2MgO (oxidation) and CuO + H₂ → Cu + H₂O (reduction).

Chemical Equation Balancing

Mistake: Failing to balance chemical equations correctly.
- Tip: Use the hit-and-trial method to ensure the number of atoms for each element is equal on both sides of the equation. Practice with equations like Fe + H₂O → Fe₃O₄ + H₂.

Types of Chemical Reactions

Mistake: Mixing up different types of reactions.
- Tip: Understand the characteristics of each type: combination, decomposition, displacement, double displacement, exothermic, and endothermic reactions.

Corrosion and Rancidity

Mistake: Not understanding the preventive measures.
- Tip: Corrosion can be prevented by painting iron articles. Rancidity is delayed by flushing food with nitrogen.

Exothermic and Endothermic Reactions

Mistake: Confusing the direction of energy flow.
- Tip: Exothermic reactions release heat (e.g., combustion), while endothermic reactions absorb heat (e.g., photosynthesis).

Chemical Reaction Indicators

Mistake: Overlooking signs of a chemical reaction.
- Tip: Look for indicators such as color change, gas production, and temperature change.

Chemical Reaction Safety

Mistake: Ignoring safety precautions.
- Tip: Always follow safety protocols, such as wearing goggles and handling chemicals with care, to prevent accidents during experiments.

CBSE Quiz & Practice Test – MCQs, True/False Questions with Solutions

Multiple Choice Questions

Decomposition reaction

Combination reaction

Displacement reaction

Double displacement reaction

Correct Answer: B

Solution:

This is a combination reaction where calcium oxide and water combine to form calcium hydroxide.

Chapter Concept:

Chemical Equation Balancing

Combination reaction

Decomposition reaction

Precipitation reaction

Redox reaction

Correct Answer: C

Solution:

The formation of a solid from two solutions indicates a precipitation reaction, where an insoluble product is formed.

Chapter Concept:

Chemical Reaction Indicators

Oxidizing agent

Reducing agent

Catalyst

Inert substance

Correct Answer: B

Solution:

Zn

acts as a reducing agent as it donates electrons to

Cu^{2+}

, reducing it to

Cu

Chapter Concept:

Oxidation and Reduction

A single reactant breaks down into two or more products.

Two reactants combine to form a single product.

An element displaces another element in a compound.

Two compounds exchange ions to form two new compounds.

Correct Answer: A

Solution:

In a decomposition reaction, a single compound breaks down into two or more simpler substances, which is the opposite of a combination reaction.

Chapter Concept:

Decomposition Reactions

To enhance the flavor of the food.

To prevent the food from becoming rancid due to oxidation.

To increase the shelf life by killing bacteria.

To add nutritional value to the food.

Correct Answer: B

Solution:

Flushing food items with nitrogen gas prevents oxidation, which can cause rancidity, thereby preserving the taste and smell of the food.

Chapter Concept:

Corrosion and Rancidity

They release heat energy.

They absorb heat energy.

They do not involve energy changes.

They always produce light.

Correct Answer: B

Solution:

Endothermic reactions absorb heat energy from the surroundings, resulting in a temperature drop.

Chapter Concept:

Exothermic and Endothermic Reactions

The reaction of calcium oxide with water to form calcium hydroxide.

The decomposition of calcium carbonate by heating.

Photosynthesis in plants.

Electrolysis of water.

Correct Answer: A

Solution:

The reaction of calcium oxide with water is exothermic as it releases heat. The equation is:

CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + \text{Heat}

Chapter Concept:

Exothermic and Endothermic Reactions

To improve taste

To prevent rancidity

To add nutrients

To make them lighter

Correct Answer: B

Solution:

Flushing with nitrogen prevents rancidity by displacing oxygen, which slows down the oxidation of fats and oils.

Chapter Concept:

Corrosion and Rancidity

Change in color

Formation of a precipitate

Evolution of a gas

All of the above

Correct Answer: D

Solution:

Chemical reactions can be identified by indicators such as change in color, formation of a precipitate, and evolution of a gas.

Chapter Concept:

Chemical Reaction Indicators

NaCl(aq) + AgNO_3(aq) \rightarrow AgCl(s) + NaNO_3(aq)

C(s) + O_2(g) \rightarrow CO_2(g)

2H_2(g) + O_2(g) \rightarrow 2H_2O(l)

CaCO_3(s) \rightarrow CaO(s) + CO_2(g)

Correct Answer: A

Solution:

A precipitation reaction is one in which an insoluble solid (precipitate) is formed. In option A,

AgCl

is the precipitate.

Chapter Concept:

Precipitation Reactions

Oxidation

Reduction

Precipitation

Displacement

Correct Answer: B

Solution:

Reduction involves the loss of oxygen or gain of hydrogen.

Chapter Concept:

Oxidation and Reduction

To enhance the appearance

To prevent corrosion

To increase weight

To make it magnetic

Correct Answer: B

Solution:

Paint is applied to iron articles to prevent corrosion by creating a barrier against moisture and oxygen.

Chapter Concept:

Corrosion and Rancidity

Zinc (

Zn

)

Hydrogen (

H_2

)

Sulfur (

S

)

Oxygen (

O_2

)

Correct Answer: B

Solution:

Zinc displaces hydrogen from sulfuric acid, producing zinc sulfate and hydrogen gas.

Chapter Concept:

Chemical Equation Balancing

Barium sulphate and sodium chloride

Barium chloride and sodium sulphate

Barium sulphate and water

Barium hydroxide and sodium chloride

Correct Answer: A

Solution:

When solutions of barium chloride and sodium sulphate are mixed, barium sulphate precipitates out and sodium chloride remains in solution:

BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)

Chapter Concept:

Precipitation Reactions

2H_2(g) + O_2(g) \rightarrow 2H_2O(l)

Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)

CaCO_3(s) \rightarrow CaO(s) + CO_2(g)

Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g)

Correct Answer: A

Solution:

In the reaction

2H_2(g) + O_2(g) \rightarrow 2H_2O(l)

, hydrogen is oxidized as it gains oxygen.

Chapter Concept:

Oxidation and Reduction

NaCl + AgNO_3 \rightarrow AgCl + NaNO_3

C + O_2 \rightarrow CO_2

2H_2 + O_2 \rightarrow 2H_2O

Fe + CuSO_4 \rightarrow FeSO_4 + Cu

Correct Answer: A

Solution:

In a double displacement reaction, ions are exchanged between two compounds. In option a,

NaCl

and

AgNO_3

exchange ions to form

AgCl

and

NaNO_3

Chapter Concept:

Displacement and Double Displacement Reactions

11.2 L

22.4 L

5.6 L

44.8 L

Correct Answer: A

Solution:

The molar mass of

CaCO_3

is 100 g/mol. Therefore, 50 g of

CaCO_3

is 0.5 moles. According to the equation, 1 mole of

CaCO_3

produces 1 mole of

CO_2

. Thus, 0.5 moles of

CaCO_3

will produce 0.5 moles of

CO_2

. At STP, 1 mole of gas occupies 22.4 L, so 0.5 moles of

CO_2

occupy 0.5 x 22.4 L = 11.2 L.

Chapter Concept:

Chemical Equation Balancing

Combination reaction

Decomposition reaction

Precipitation reaction

Redox reaction

Correct Answer: C

Solution:

This is a precipitation reaction because

AgCl(s)

is formed as an insoluble solid (precipitate) from the reaction of two aqueous solutions.

Chapter Concept:

Precipitation Reactions

5 moles

8 moles

6 moles

10 moles

Correct Answer: A

Solution:

The reaction shows that 2 moles of

Fe

react with 3 moles of

Cl_2

to produce 2 moles of

FeCl_3

. Therefore, 5 moles of

Fe

will react with 7.5 moles of

Cl_2

to produce 5 moles of

FeCl_3

. Since only 8 moles of

Cl_2

are available,

Fe

is the limiting reagent, and 5 moles of

FeCl_3

will be produced.

Chapter Concept:

Chemical Equation Balancing

Zinc (

Zn

)

Copper (

Cu

)

Sulfate (

SO_4

)

None of the above

Correct Answer: B

Solution:

Zinc displaces copper because

Zn

is more reactive than

Cu

Chapter Concept:

Types of Chemical Reactions

BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)

Zn(s) + 2HCl(aq) \rightarrow ZnCl_2(aq) + H_2(g)

C_6H_{12}O_6(aq) + 6O_2(g) \rightarrow 6CO_2(g) + 6H_2O(l)

2H_2(g) + O_2(g) \rightarrow 2H_2O(l)

Correct Answer: A

Solution:

A precipitation reaction involves the formation of an insoluble solid (precipitate) from two aqueous solutions. In option a,

BaSO_4(s)

is the precipitate formed.

Chapter Concept:

Precipitation Reactions

1 gram

2 grams

0.5 grams

4 grams

Correct Answer: A

Solution:

According to the equation, 2 moles of

K

produce 1 mole of

H_2

. Therefore, 0.5 moles of

K

will produce 0.25 moles of

H_2

. The molar mass of

H_2

is 2 g/mol, so 0.25 moles of

H_2

weigh 0.25 x 2 g = 0.5 g.

Chapter Concept:

Chemical Equation Balancing

2H_2O_2 \rightarrow 2H_2O + O_2

C + O_2 \rightarrow CO_2

Zn + 2HCl \rightarrow ZnCl_2 + H_2

CaO + H_2O \rightarrow Ca(OH)_2

Correct Answer: A

Solution:

A decomposition reaction involves a single compound breaking down into two or more simpler substances. In option a,

H_2O_2

decomposes into

H_2O

and

O_2

Chapter Concept:

Types of Chemical Reactions

Zinc hydroxide and hydrogen gas

Zinc chloride and hydrogen gas

Zinc oxide and water

Zinc sulfate and water

Correct Answer: B

Solution:

The reaction of zinc with hydrochloric acid produces zinc chloride and hydrogen gas:

Zn + 2HCl \rightarrow ZnCl_2 + H_2

Chapter Concept:

Displacement and Double Displacement Reactions

2H_2 + O_2 \rightarrow 2H_2O

H_2 + O_2 \rightarrow H_2O

H_2 + O_2 \rightarrow 2H_2O

2H_2 + O_2 \rightarrow H_2O

Correct Answer: A

Solution:

Option A is balanced because there are 4 hydrogen atoms and 2 oxygen atoms on both sides of the equation.

Chapter Concept:

Chemical Equation Balancing

Combination reaction

Decomposition reaction

Displacement reaction

Double displacement reaction

Correct Answer: C

Solution:

The reaction between zinc and copper sulfate is a displacement reaction. Zinc displaces copper from copper sulfate, forming zinc sulfate and copper metal, which appears as a reddish-brown solid. The reaction can be represented as:

Zn + CuSO_4 \rightarrow ZnSO_4 + Cu

Chapter Concept:

Types of Chemical Reactions

BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)

H_2 + Cl_2 \rightarrow 2HCl

2H_2O \rightarrow 2H_2 + O_2

C + O_2 \rightarrow CO_2

Correct Answer: A

Solution:

In option a,

BaSO_4

is an insoluble salt that precipitates out of the solution, making it a precipitation reaction.

Chapter Concept:

Displacement and Double Displacement Reactions

CaCO_3(s) \rightarrow CaO(s) + CO_2(g)

2H_2(g) + O_2(g) \rightarrow 2H_2O(l)

C(s) + O_2(g) \rightarrow CO_2(g)

Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)

Correct Answer: A

Solution:

In a decomposition reaction, a single compound breaks down into two or more substances. The reaction

CaCO_3(s) \rightarrow CaO(s) + CO_2(g)

is a decomposition reaction where heat is supplied.

Chapter Concept:

Decomposition Reactions

Carbon is being oxidized.

Carbon is being reduced.

Carbon is neither oxidized nor reduced.

Carbon is both oxidized and reduced.

Correct Answer: A

Solution:

Carbon is being oxidized as it gains oxygen to form carbon dioxide.

Chapter Concept:

Oxidation and Reduction

Endothermic reaction

Exothermic reaction

Displacement reaction

Precipitation reaction

Correct Answer: B

Solution:

Respiration is an exothermic reaction because it releases energy. The reaction is:

C_6H_{12}O_6(aq) + 6O_2(aq) \rightarrow 6CO_2(aq) + 6H_2O(l) + \text{Energy}

Chapter Concept:

Exothermic and Endothermic Reactions

Hydrogen gas and iron chloride are produced.

Chlorine gas and iron hydroxide are produced.

No reaction takes place.

Iron salt and water are produced.

Correct Answer: A

Solution:

When dilute hydrochloric acid is added to iron fillings, hydrogen gas and iron chloride are produced.

Chapter Concept:

Chemical Reaction Indicators

An iron nail left in a humid environment develops a reddish-brown coating over time.

A piece of wood is burned and turns to ash.

A sugar cube dissolves in water.

A balloon is inflated with air.

Correct Answer: A

Solution:

Corrosion is the process where metals are gradually degraded by chemical reactions with environmental elements. The reddish-brown coating on an iron nail is rust, a common result of corrosion.

Chapter Concept:

Corrosion and Rancidity

2H_2 + O_2 \rightarrow 2H_2O

2HgO \rightarrow 2Hg + O_2

Fe + CuSO_4 \rightarrow FeSO_4 + Cu

Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 + 2NaCl

Correct Answer: A

Solution:

A combination reaction involves two or more substances combining to form a single product. In option a, hydrogen and oxygen combine to form water.

Chapter Concept:

Types of Chemical Reactions

Lead (

Pb

)

Carbon (

C

)

Carbon dioxide (

CO_2

)

Lead oxide (

PbO

)

Correct Answer: B

Solution:

Carbon is oxidized as it gains oxygen to form carbon dioxide.

Chapter Concept:

Oxidation and Reduction

CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq)

2H_2O(l) \rightarrow 2H_2(g) + O_2(g)

Zn + CuSO_4 \rightarrow ZnSO_4 + Cu

2PbO(s) + C(s) \rightarrow 2Pb(s) + CO_2(g)

Correct Answer: A

Solution:

A combination reaction involves two or more substances combining to form a single product. In option a, calcium oxide and water combine to form calcium hydroxide.

Chapter Concept:

Types of Chemical Reactions

Combination reaction

Decomposition reaction

Displacement reaction

Double displacement reaction

Correct Answer: C

Solution:

This is a displacement reaction where iron displaces copper from copper sulfate to form iron sulfate and copper.

Chapter Concept:

Displacement and Double Displacement Reactions

Endothermic reaction

Exothermic reaction

Precipitation reaction

Displacement reaction

Correct Answer: B

Solution:

An increase in temperature indicates that heat is being released, which is characteristic of an exothermic reaction.

Chapter Concept:

Chemical Reaction Indicators

The solution changes color.

Bubbles of gas are produced.

The temperature of the solution decreases.

The metal dissolves without any visible change.

Correct Answer: B

Solution:

The production of gas bubbles is a clear indicator of a chemical reaction occurring, as it signifies the release of a gaseous product.

Chapter Concept:

Chemical Reaction Indicators

Electrolysis of water to form hydrogen and oxygen gases.

Heating of calcium carbonate to form calcium oxide and carbon dioxide.

Burning of magnesium ribbon in air to form magnesium oxide.

Reaction of zinc with hydrochloric acid to form zinc chloride and hydrogen gas.

Correct Answer: A

Solution:

The electrolysis of water is a decomposition reaction where water is broken down into hydrogen and oxygen gases using electricity.

Chapter Concept:

Decomposition Reactions

Cu(s) + 2AgNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + 2Ag(s)

2Cu(s) + AgNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + Ag(s)

Cu(s) + AgNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + 2Ag(s)

Cu(s) + 2AgNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + Ag(s)

Correct Answer: A

Solution:

Copper displaces silver from silver nitrate solution, forming copper(II) nitrate and silver.

Chapter Concept:

Oxidation and Reduction

CaCO_3(s) \rightarrow CaO(s) + CO_2(g)

2H_2O(l) \rightarrow 2H_2(g) + O_2(g)

2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)

2NaCl(s) \rightarrow 2Na(s) + Cl_2(g)

Correct Answer: C

Solution:

The reaction

2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)

is a decomposition reaction where potassium chlorate decomposes into potassium chloride and oxygen gas upon heating.

Chapter Concept:

Decomposition Reactions

Combination reaction

Decomposition reaction

Displacement reaction

Double displacement reaction

Correct Answer: B

Solution:

A decomposition reaction involves a single compound breaking down into two or more simpler substances. Here, water decomposes into hydrogen and oxygen.

Chapter Concept:

Types of Chemical Reactions

C(s) + O_2(g) \rightarrow CO_2(g)

2H_2O(l) \rightarrow 2H_2(g) + O_2(g)

BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)

CaCO_3(s) \rightarrow CaO(s) + CO_2(g)

Correct Answer: A

Solution:

An exothermic reaction releases heat. The burning of coal (carbon) in oxygen to form carbon dioxide is exothermic.

Chapter Concept:

Types of Chemical Reactions

22.4 L

44.8 L

11.2 L

33.6 L

Correct Answer: B

Solution:

Molar mass of

NH_3

is 17 g/mol. Therefore, 17 g of

NH_3

is 1 mole. According to the balanced equation, 4 moles of

NH_3

require 5 moles of

O_2

. Thus, 1 mole of

NH_3

will require 1.25 moles of

O_2

. At STP, 1 mole of gas occupies 22.4 L, so 1.25 moles of

O_2

occupy 1.25 x 22.4 L = 28 L.

Chapter Concept:

Chemical Equation Balancing

3:4

4:3

1:1

2:3

Correct Answer: A

Solution:

The balanced equation shows that 3 moles of

CO_2

are produced for every 4 moles of

H_2O

. Therefore, the ratio of moles of

CO_2

H_2O

is 3:4.

Chapter Concept:

Chemical Equation Balancing

4Na(s) + O_2(g) \rightarrow 2Na_2O(s)

CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O(l)

2H_2(g) + O_2(g) \rightarrow 2H_2O(l)

Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)

Correct Answer: A

Solution:

In the reaction

4Na(s) + O_2(g) \rightarrow 2Na_2O(s)

, sodium is oxidized as it gains oxygen.

Chapter Concept:

Oxidation and Reduction

Zn + 2HCl \rightarrow ZnCl_2 + H_2

2Na + Cl_2 \rightarrow 2NaCl

AgNO_3 + NaCl \rightarrow AgCl + NaNO_3

C + O_2 \rightarrow CO_2

Correct Answer: C

Solution:

In a double displacement reaction, two compounds exchange ions to form two new compounds. Option c shows

AgNO_3

and

NaCl

exchanging ions to form

AgCl

and

NaNO_3

Chapter Concept:

Displacement and Double Displacement Reactions

Zn + CuSO_4 \rightarrow ZnSO_4 + Cu

2H_2 + O_2 \rightarrow 2H_2O

CaO + H_2O \rightarrow Ca(OH)_2

2PbO + C \rightarrow 2Pb + CO_2

Correct Answer: A

Solution:

In a displacement reaction, one element displaces another in a compound. In option a,

Zn

displaces

Cu

from

CuSO_4

Chapter Concept:

Displacement and Double Displacement Reactions

Combination reaction

Decomposition reaction

Displacement reaction

Double displacement reaction

Correct Answer: C

Solution:

This is a displacement reaction where zinc displaces copper from copper sulfate, forming zinc sulfate and copper.

Chapter Concept:

Types of Chemical Reactions

To ensure the equation is aesthetically pleasing.

To comply with the law of conservation of mass.

To make the equation easier to read.

To increase the number of products.

Correct Answer: B

Solution:

Balancing a chemical equation ensures that the number of atoms for each element is the same on both sides, complying with the law of conservation of mass.

Chapter Concept:

Chemical Equation Balancing

2H_2O(l) \rightarrow 2H_2(g) + O_2(g)

H_2(g) + Cl_2(g) \rightarrow 2HCl(g)

NaCl(aq) + AgNO_3(aq) \rightarrow AgCl(s) + NaNO_3(aq)

C(s) + O_2(g) \rightarrow CO_2(g)

Correct Answer: A

Solution:

The reaction

2H_2O(l) \rightarrow 2H_2(g) + O_2(g)

is a decomposition reaction as water decomposes into hydrogen and oxygen gases.

Chapter Concept:

Decomposition Reactions

Copper(II) oxide (

CuO

)

Hydrogen (

H_2

)

Copper (

Cu

)

Water (

H_2O

)

Correct Answer: A

Solution:

Copper(II) oxide is reduced to copper as it loses oxygen.

Chapter Concept:

Oxidation and Reduction

2H_2O(l) \rightarrow 2H_2(g) + O_2(g)

CaCO_3(s) \rightarrow CaO(s) + CO_2(g)

2NaCl(l) \rightarrow 2Na(s) + Cl_2(g)

C(s) + O_2(g) \rightarrow CO_2(g)

Correct Answer: C

Solution:

The reaction

2NaCl(l) \rightarrow 2Na(s) + Cl_2(g)

is an example of electrolysis, where electricity is used to decompose molten sodium chloride into sodium and chlorine gas.

Chapter Concept:

Decomposition Reactions

CaO + H_2O \rightarrow Ca(OH)_2 + \text{heat}

2NaHCO_3 \rightarrow Na_2CO_3 + CO_2 + H_2O

N_2 + O_2 \rightarrow 2NO

NH_4NO_3 \rightarrow N_2O + 2H_2O

Correct Answer: A

Solution:

Solution:

An exothermic reaction is characterized by the release of energy, typically in the form of heat, making the surroundings warmer. In contrast, an endothermic reaction absorbs energy from the surroundings.

Chapter Concept :

Exothermic and Endothermic Reactions

Chemical Reactions and Equations

AI Learning Assistant

CBSE Learning Objectives – Key Concepts & Skills You Must Know

Learning Objectives

CBSE Revision Notes & Quick Summary for Last-Minute Study

Chapter Notes

Decomposition Reactions

Displacement and Double Displacement Reactions

Precipitation Reactions

Oxidation and Reduction

Chemical Equation Balancing

Types of Chemical Reactions

Corrosion and Rancidity

Exothermic and Endothermic Reactions

Chemical Reaction Indicators

Chemical Reaction Safety

CBSE Exam Tips, Important Questions & Common Mistakes to Avoid

Common Mistakes & Exam Tips

Decomposition Reactions

Displacement and Double Displacement Reactions

Precipitation Reactions

Oxidation and Reduction

Chemical Equation Balancing

Types of Chemical Reactions

Corrosion and Rancidity

Exothermic and Endothermic Reactions

Chemical Reaction Indicators

Chemical Reaction Safety

Multiple Choice Questions

Q1.What type of reaction is represented by CaO(s)+H2O(l)→Ca(OH)2(aq)CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq)CaO(s)+H2​O(l)→Ca(OH)2​(aq)?

Correct Answer: B

Q2.A student performs a reaction where a solid forms when two clear solutions are mixed. What type of reaction is this?

Correct Answer: C

Q3.What is the role of ZnZnZn in the reaction Zn+CuSO4→ZnSO4+CuZn + CuSO_4 \rightarrow ZnSO_4 + CuZn+CuSO4​→ZnSO4​+Cu?

Correct Answer: B

Q4.Which of the following is a characteristic of a decomposition reaction?

Correct Answer: A

Q5.Why are oil and fat containing food items often flushed with nitrogen gas?

Correct Answer: B

Q6.Which statement is true about endothermic reactions?

Correct Answer: B

Q7.Which of the following reactions is an example of an exothermic reaction?

Correct Answer: A

Q8.Why are oil and fat containing food items flushed with nitrogen?

Correct Answer: B

Q9.Which of the following is an indicator of a chemical reaction taking place?

Correct Answer: D

Q10.Which of the following reactions is an example of a precipitation reaction?

Correct Answer: A

Q11.Which process involves the loss of oxygen?

Correct Answer: B

Q12.What is the primary reason for applying paint on iron articles?

Correct Answer: B

Q13.In the reaction Zn+H2SO4→ZnSO4+H2Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2Zn+H2​SO4​→ZnSO4​+H2​, which element is displaced?

Correct Answer: B

Q14.What is formed when solutions of barium chloride and sodium sulphate are mixed?

Correct Answer: A

Q15.Which of the following reactions is an example of oxidation?

Correct Answer: A

Q16.Which of the following reactions is a double displacement reaction?

Correct Answer: A

Q17.For the reaction CaCO3(s)→CaO(s)+CO2(g)CaCO_3(s) \rightarrow CaO(s) + CO_2(g)CaCO3​(s)→CaO(s)+CO2​(g), if 50 grams of CaCO3CaCO_3CaCO3​ decompose completely, what volume of CO2CO_2CO2​ gas at STP will be produced?

Correct Answer: A

Q18.Consider the reaction: AgNO3(aq)+NaCl(aq)→AgCl(s)+NaNO3(aq)AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)AgNO3​(aq)+NaCl(aq)→AgCl(s)+NaNO3​(aq). What type of chemical reaction is this?

Correct Answer: C

Q19.Consider the reaction: 2Fe+3Cl2→2FeCl32Fe + 3Cl_2 \rightarrow 2FeCl_32Fe+3Cl2​→2FeCl3​. If 5 moles of FeFeFe are reacted with 8 moles of Cl2Cl_2Cl2​, how many moles of FeCl3FeCl_3FeCl3​ will be produced?

Correct Answer: A

Q20.In the reaction Zn+CuSO4→ZnSO4+CuZn + CuSO_4 \rightarrow ZnSO_4 + CuZn+CuSO4​→ZnSO4​+Cu, which element is displaced?

Correct Answer: B

Q21.Which of the following reactions is an example of a precipitation reaction?

Correct Answer: A

Q22.Given the reaction 2K+2H2O→2KOH+H22K + 2H_2O \rightarrow 2KOH + H_22K+2H2​O→2KOH+H2​, if 0.5 moles of KKK are reacted with excess water, how many grams of H2H_2H2​ will be produced?

Correct Answer: A

Q23.Which of the following reactions is an example of a decomposition reaction?

Correct Answer: A

Q24.What is the product formed when zinc reacts with hydrochloric acid?

Correct Answer: B

Q25.Which of the following is a balanced chemical equation?

Correct Answer: A

Q26.A student performs an experiment where they add a piece of zinc to a solution of copper sulfate. After some time, they observe the formation of a reddish-brown solid and the solution becomes colorless. What type of chemical reaction is occurring in this experiment?