Question

Give one example each of a chemical reaction showing the following characteristics.

(a) evolution of a gas
(b) change of colour
(c) formation of precipitate
(d) change of state from liquid to gas
(e) change of state from gas to liquid

Answer 1

(a) Zn + H₂SO₄ → ZnSO₄ + H₂↑
​ Zinc Sulphuric Zinc Hydrogen
acid sulphate
(b) CuCO₃ → CuO + CO₂↑​
Copper Copper Carbon
carbonate oxide dioxide
(green) (black)

(c) CuSO₄ + H₂S → CuS↓ + H₂SO_4
​ Copper Hydrogen Copper Sulphuric
sulphate sulphide sulphide acid

(d) 2H₂O (l) → 2H₂ (g) + O₂ (g)
Water Hydrogen Oxygen

(e) ​2H₂ (g) + O₂ (g) → 2H₂O (l)
Hydrogen Oxygen Water