Endothermic and exothermic reaction

Exothermic reaction – heat is evolved during a reaction. Most of the combination reactions are exothermic.

Al + Fe₂O₃ → Al₂O₃ + Fe + heat
CH₄ + 2O₂ → CO₂ + 2H₂O + heat

Effect of oxidation reaction in everyday life

Endothermic – Heat is required to carry out the reaction.

6CO₂ + 6H₂O + Sunlight → C₆H₁₂O₆ + 6O₂

Glucose
Most of the decomposition reactions are endothermic.

Corrosion

Gradual deterioration of a material, usually a metal, by the action of moisture, air or chemicals in the surrounding environment.

Rusting:

4Fe(s) + 3O₂(from air) + xH₂O(moisture) → 2Fe₂O₃.xH₂O(rust)
Corrosion of copper:
Cu(s) + H₂O(moisture) + CO₂(from air) → CuCO₃.Cu(OH)₂(green)
Corrosion of silver:
Ag(s) + H₂S (from air) → Ag₂S(black) + H₂(g)

Rancidity

It refers to the oxidation of fats and oils in food that is kept for a long time. It gives foul smell and bad taste to food. Rancid food causes stomach infection on consumption.
Prevention:
(i) Use of air-tight containers
(ii) Packaging with nitrogen
(iii) Refrigeration
(iv) Addition of antioxidants or preservatives