Chemical Reactions and Equations – Class 10 Chemistry Chapter 1

Chemical Reactions and Equations

A chemical reaction is a process in which one or more substances (reactants) are converted into one or more different substances (products). Chemical reactions are accompanied by changes in energy, colour, state, or the evolution of gas.

Writing Chemical Equations

A chemical equation represents a chemical reaction using symbols and formulae. For example:

Mg + O₂ → MgO

The substances on the left are reactants, and those on the right are products.

Balancing Chemical Equations

According to the Law of Conservation of Mass, mass can neither be created nor destroyed. Therefore, the number of atoms of each element must be equal on both sides of the equation.

Steps to balance:

1. Write the unbalanced equation with correct formulae.
2. List the number of atoms of each element on both sides.
3. Start balancing with the compound that has the maximum number of atoms.
4. Use coefficients (not subscripts) to balance.
5. Verify that all elements are balanced.

Example: Fe + H₂O → Fe₃O₄ + H₂

Balanced: 3Fe + 4H₂O → Fe₃O₄ + 4H₂

Types of Chemical Reactions

Type	Description	Example
Combination	Two or more reactants form a single product	CaO + H₂O → Ca(OH)₂
Decomposition	Single reactant breaks into multiple products	2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
Displacement	More reactive element displaces a less reactive one	Fe + CuSO₄ → FeSO₄ + Cu
Double Displacement	Exchange of ions between two compounds	Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
Redox	Simultaneous oxidation and reduction	CuO + H₂ → Cu + H₂O

Oxidation and Reduction

• Oxidation: Gain of oxygen or loss of hydrogen.
• Reduction: Loss of oxygen or gain of hydrogen.

A reaction where both oxidation and reduction occur simultaneously is called a redox reaction.

Effects of Oxidation in Everyday Life

• Corrosion: Iron reacts with oxygen and moisture to form rust (Fe₂O₃·xH₂O). Silver turns black due to formation of Ag₂S. Copper develops a green coating of CuCO₃.
• Rancidity: Fats and oils oxidise over time, making food smell and taste bad. Prevented by adding antioxidants, storing in airtight containers, or flushing with nitrogen gas.

Key Formulas to Remember

Balanced equations of all types should be practised extensively. Focus on identifying the type of reaction and the oxidising/reducing agents.

Reference: NCERT Science Textbook for Class 10 – Chapter 1; Lakhmir Singh & Manjit Kaur Chemistry for Class 10.