Chemical Reactions and Equations

 1. Chemical Reactions and Equations

Chemical Reaction

A process in which new substances are formed with different properties.

Indicators of Chemical Reaction:

∙ Change in color

∙ Evolution of gas

∙ Formation of precipitate

∙ Change in temperature

∙ Change in state

Chemical Equation

Symbolic representation of a chemical reaction.

∙ Unbalanced equation: Zn + HCl → ZnCl₂ + H₂

∙ Balanced equation: Zn + 2HCl → ZnCl₂ + H₂

Types of Chemical Reactions:

1. Combination Reaction

Two or more substances combine to form a single product.

∙ Example: CaO + H₂O → Ca(OH)₂

∙ Example: C + O₂ → CO₂

2. Decomposition Reaction

A single substance breaks down into two or more products.

∙ Thermal decomposition: 2FeSO₄ →(heat) Fe₂O₃ + SO₂ + SO₃

∙ Electrolytic decomposition: 2H₂O →(electricity) 2H₂ + O₂

∙ Photochemical decomposition: 2AgCl →(sunlight) 2Ag + Cl₂

3. Displacement Reaction

A more reactive element displaces a less reactive element from its compound.

∙ Example: Zn + CuSO₄ → ZnSO₄ + Cu

∙ Example: Fe + CuSO₄ → FeSO₄ + Cu

4. Double Displacement Reaction

Exchange of ions between two compounds.

∙ Example: Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl

∙ Example: AgNO₃ + NaCl → AgCl↓ + NaNO₃

5. Oxidation-Reduction (Redox) Reactions

∙ Oxidation: Addition of oxygen OR removal of hydrogen

∙ Reduction: Removal of oxygen OR addition of hydrogen

∙ Example: CuO + H₂ → Cu + H₂O (CuO is reduced, H₂ is oxidized)

Important Terms:

∙ Corrosion: Deterioration of metals due to atmospheric action (rusting of iron)

∙ Rancidity: Oxidation of fats and oils causing bad smell and taste