Question

Give three examples each of chemical changes with the following characteristics :- 1. Change in colour. 2. Evolution of a gas. 3. Change in state. 4. Formation of a precipitate. 5. Evolution of heat.

Answer 1

Dear student ,

1. Evolution of gas:
(NH₄)₂SO₄ (aq) + Ca (OH)₂ (aq) → CaSO₄(s) + 2H₂O(l) + 2NH₃(g)
When acids react with water hydrogen gas is liberated.
CaCO₃ + 2HCl $\to$CaCl₂ + CO₂ + H₂O

2. Change in colour :
Rusting of iron , colour of iron changes to reddish brown when rusting happens.
CuSO₄ + Fe → FeSO₄ + Cu
When calcium carbonate reacts with carbon dioxide it forms a yellow substance.

3. Change in state - burning of paper and melting of ice

4. Formation of a precipitate :
AgNO₃ + KCl → AgCl + KNO₃

5. Evolution of heat :
When calcium oxide reacts with water a lot of heat is evolved.
BaSO₄ + 2NH₄Cl → BaCl₂ + (NH₄)₂SO₄

Regards



2HCl + CaCO3 → CaCl2 + CO2 + H2O