What is a Gas Evolution Reaction

A gas evolution reaction is a chemical reaction in which one of the products is a gas, such as hydrogen, oxygen, and carbon dioxide. For example, the oxidation of metal in an acidic solution will yield a metal salt and hydrogen. The reaction is generally carried out in an enclosed chamber if the gases are toxic ^[1-3].

Examples of Gas Evolution Reaction

Here are some examples of chemical reactions showing the evolution of gas ^[1-4].

1. When sodium sulfate (Na₂SO₃) reacts with hydrochloric acid (HCl), the reaction produces sodium chloride (NaCl), water (H₂O), and sulfur dioxide (SO₂).

Na₂SO₃ (aq.) + 2 HCl (aq.) → 2 NaCl (aq.) + H₂O (l) + SO₂ (g)

2. Hydrochloric acid (HCl) reacts with calcium carbonate (CaCO₃) to form calcium chloride (CaCl₂), carbon dioxide (CO₂), and water (H₂O).

CaCO₃ (aq.) + 2 HCl (aq.) → CaCl₂ (aq.) + H₂O (l) + CO₂ (s)

3. Zinc (Zn) displaces and releases hydrogen (H₂) from sulfuric acid (H₂SO₄). This is an example of a single-replacement reaction.

Zn (s) + H₂SO₄ (aq.) → ZnSO₄ (aq.) + H₂ (g)

4. Gaseous hydrogen chloride (HCl) and fluorine (F₂) gas react to release chlorine (Cl₂) gas

F₂ (g) + 2 HCl (g) → 2 HF (g) + Cl₂ (g)

5. Hydrochloric acid (HCl) readily decomposes sodium sulfide (Na₂S) with the evolution of hydrogen sulfide (H₂S) gas.

Na₂S (aq.) + 2 HCl (aq.) → 2 NaCl (aq.) + H₂S (g)

6. Upon heating, ferrous sulfate (FeSO₄) decomposes to produce ferric oxide (Fe₂O₃), sulfur dioxide (SO₂) and sulfur trioxide (SO₃)

2 FeSO₄ (s) → Fe₂O₃ (s) + SO₂ (g) + SO₃ (g)