Class 10 Science Chapter 1: Chemical Reactions and Equations

Introduction to Chemical Reactions

A chemical reaction is a process in which one or more substances, called reactants, are converted to one or more different substances, called products. Substances are either chemical elements or compounds.

A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

Chemical Equations

A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formulae, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side.

For example, when hydrogen gas (H₂) reacts with oxygen gas (O₂), they form water (H₂O).

Types of Chemical Reactions

1. Combination Reaction: Two or more substances combine to form a new single substance.

   Example: C + O₂ → CO₂

2. Decomposition Reaction: A single substance decomposes to give two or more substances.

   Example: 2H₂O → 2H₂ + O₂

3. Displacement Reaction: A more reactive element displaces a less reactive element from its compound.

   Example: Fe + CuSO₄ → FeSO₄ + Cu

4. Double Displacement Reaction: When two compounds react and exchange their ions to form two new compounds.

   Example: NaOH + HCl → NaCl + H₂O

5. Redox Reaction: Reactions that involve both reduction and oxidation processes.

   Example: ZnO + C → Zn + CO

Balancing Chemical Equations

According to the Law of Conservation of Mass, mass can neither be created nor destroyed in a chemical reaction. Therefore, the total mass of elements present in reactants must be equal to the total mass of elements present in products.

Steps to balance a chemical equation:

1. Write the correct formulae of reactants and products.
2. Count the number of atoms of each element present in the unbalanced equation.
3. Balance the equation by using appropriate coefficients.
4. Check if the number of atoms of each element is balanced on both sides.

Effects of Oxidation Reactions in Everyday Life

• Corrosion: When a metal is attacked by substances around it such as moisture, acids, etc.
• Rancidity: The oxidation of fats and oils in food that causes them to become rancid and develop an unpleasant taste and smell.