I. Chemical Equations for the Thermal Decomposition of Ammonium Bicarbonate
Thermal Decomposition Equation:
NH₄HCO₃ → NH₃↑ + H₂O + CO₂↑ (Δ indicates heating).
Related Chemical Reactions:
Reaction with hydrochloric acid:
NH₄HCO₃ + HCl → NH₄Cl + H₂O + CO₂↑
Reaction with sulfuric acid:
With excess H₂SO₄:
H₂SO₄ (excess) + NH₄HCO₃ → H₂O + CO₂↑ + NH₄HSO₄
With excess NH₄HCO₃:
H₂SO₄ + 2NH₄HCO₃ (excess) → 2H₂O + 2CO₂↑ + (NH₄)₂SO₄
Reaction with sodium hydroxide:
With limited NaOH:
2NH₄HCO₃ + 2NaOH (limited) → (NH₄)₂CO₃ + Na₂CO₃ + 2H₂O
With excess NaOH:
NH₄HCO₃ + 2NaOH (excess) → Na₂CO₃ + H₂O + NH₃·H₂O
Heating conditions:
NH₄HCO₃ + 2NaOH → NH₃↑ + Na₂CO₃ + 2H₂O
II. Thermal Decomposition Temperature of Ammonium Bicarbonate
Ammonium bicarbonate (NH₄HCO₃) is a white crystalline solid with the following properties:
Aqueous solution is alkaline.
Chemically unstable and readily decomposes when heated.
Decomposition Behavior at Different Temperatures:
Below 10°C:
Chemically stable; minimal decomposition.
10–20°C:
Decomposition is insignificant.
Above 30°C:
Rapid decomposition into CO₂, NH₃, and H₂O.
At 60°C:
Complete decomposition.
III. Phenomena and Explanation of Ammonium Bicarbonate Thermal Decomposition
Phenomenon:
When ammonium bicarbonate (NH₄HCO₃) is heated, the white solid gradually disappears, and a colorless gas with a pungent odor is produced.
Explanation of the Phenomenon:
Chemical Reaction:
Under heating, ammonium bicarbonate decomposes into three products:
NH₄HCO₃ → NH₃↑ + H₂O + CO₂↑
Observed Changes:
Ammonium bicarbonate (white solid):
The original solid dissolves and gradually disappears during decomposition.
Ammonia gas (NH₃):
A colorless gas with a strong, irritating odor (responsible for the observed smell).
Carbon dioxide (CO₂):
A colorless and odorless gas that does not contribute to the visible or olfactory phenomena