Chemical Reactions and Equations — Maharashtra (SSC) Class 10 Science Solutions (Free)

Chemical reaction: A process in which reactants are transformed into products with breaking and formation of chemical bonds. Chemical equation: A symbolic representation of a chemical reaction using chemical formulas and coefficients. Balancing: Adjusting coefficients so that number of atoms of each element is equal on both sides. Balanced equation shows the correct molar ratios of reactants and products.

Step 1: Count atoms on both sides: Fe: 1 left, 2 right; O: 2 left, 3 right Step 2: Balance Fe: Multiply Fe by 4 and Fe2O3 by 2 -> 4Fe + O2 -> 2Fe2O3 Step 3: Count O: Left has 2, right has 6 (2 x 3). Multiply O2 by 3 Step 4: 4Fe + 3O2 -> 2Fe2O3 Step 5: Verify: Fe = 4 on both sides, O = 6 on both sides. Balanced.

(1) Decomposition reaction: Single reactant breaks into multiple products due to heat. (2) Combination or synthesis reaction: Two reactants combine to form one product. (3) Displacement or double displacement reaction: Ions exchange partners. Ag+ exchanges with Na+, Cl- exchanges with NO3-. AgCl is precipitate (insoluble). All are irreversible reactions in forward direction.

Redox reaction: A reaction in which oxidation and reduction occur simultaneously. Oxidation: Loss of electrons (or gain of oxygen or loss of hydrogen). Reduction: Gain of electrons (or loss of oxygen or gain of hydrogen). Example: 2Cu + O2 -> 2CuO. Here, Cu loses electrons (oxidized), O2 gains electrons (reduced). Oxidizing agent: Substance that causes oxidation (O2). Reducing agent: Substance that causes reduction (Cu).

Step 1: Determine oxidation states. Zn: 0 -> +2 (loses 2 electrons, oxidized). Cu: +2 -> 0 (gains 2 electrons, reduced). Step 2: Oxidation occurs at Zn atom (reducing agent). Reduction occurs at Cu atom (oxidizing agent). Step 3: Electrons lost by Zn = electrons gained by Cu = 2 electrons. This is a displacement reaction where more reactive Zn displaces Cu from its compound.