Class 10 Science Chapter 1, Chemical Reactions and Equations, explains how substances change into new substances through chemical reactions.

In Class 10 Science Chapter 1, students learn about chemical reactions and their types…””The first chapter of Class 10 Science includes combination and decomposition reactions.

1 Mark Questions

Q1. Define a chemical reaction.
Ans: A chemical reaction is a process in which one or more substances (reactants) are converted into new substances (products) with new properties.

Q2. Write the chemical equation for the reaction of magnesium with oxygen.
Ans:

2Mg + O_2 rightarrow 2MgO

Q3. What is meant by a balanced chemical equation?
Ans: A chemical equation in which the number of atoms of each element is equal on both sides is called a balanced chemical equation.

Q4. Name the gas evolved when zinc reacts with dilute hydrochloric acid.
Ans: Hydrogen gas (H₂) is evolved.

Q5. Write one example of a redox reaction.
Ans:

Zn + CuSO_4 rightarrow ZnSO_4 + Cu

2 Mark Questions

Q1. Why is it important to balance a chemical equation?
Ans: To follow the Law of Conservation of Mass, which states that mass can neither be created nor destroyed in a chemical reaction.

Q2. What is rancidity? How can it be prevented?
Ans: Rancidity is the spoilage of food containing fats and oils due to oxidation. It can be prevented by:

Storing in airtight containers

Using antioxidants

Refrigeration

Q3. Write a balanced chemical equation for the thermal decomposition of lead nitrate.
Ans:

2Pb(NO_3)_2 xrightarrow{heat} 2PbO + 4NO_2 + O_2

Q4. Define oxidation and reduction with examples.
Ans:

Oxidation: Gain of oxygen or loss of hydrogen (e.g., )

Reduction: Loss of oxygen or gain of hydrogen (e.g., )

3 Mark Questions

Q1. Differentiate between displacement and double displacement reaction.
Ans:

Displacement Reaction Double Displacement Reaction

One element replaces another Exchange of ions between compounds

Q2. Write balanced chemical equations for the following:

a. Decomposition of ferrous sulphate:

2FeSO_4 xrightarrow{heat} Fe_2O_3 + SO_2 + SO_3

b. Reaction of zinc with copper sulphate:

Zn + CuSO_4 rightarrow ZnSO_4 + Cu

c. Reaction of barium chloride with sodium sulphate:

BaCl_2 + Na_2SO_4 rightarrow BaSO_4 + 2NaCl

Q3. What is corrosion? Write the chemical reaction involved in the rusting of iron.
Ans: Corrosion is the slow destruction of metals due to reaction with moisture, air, etc.
Rusting of iron:

4Fe + 3O_2 + 6H_2O rightarrow 4Fe(OH)_3

5 Mark Question Example

Q1. Define combination, decomposition, and displacement reactions. Give one example of each.
Ans:

Combination:
Two or more substances combine to form a single product.

Decomposition:
A single compound breaks into simpler compounds. Displacement:
A more reactive element displaces a less reactive one.

Official NCERT Class 10 Science