- 2067 Chaitra · 1+2+2 marks
Catalyst; positive and negative catalysis with examples
Short answer
A catalyst changes reaction rate without being consumed. Positive catalysts like MnO₂ in KClO₃ decomposition and Fe in ammonia synthesis increase rate by lowering activation energy. Negative catalysts like glycerol in H₂O₂ decomposition and alcohol in Na₂SO₃ oxidation decrease rate.
What is catalyst? Explain positive and negative catalysis with two examples for each.
Catalyst
A catalyst is a substance that changes the rate of a chemical reaction without being consumed in the reaction (its mass and chemical nature are the same at the end). The phenomenon is called catalysis. Example: MnO₂ speeds up the decomposition of KClO₃ to O₂.
Positive catalysis
The catalyst increases the rate of the reaction by lowering the activation energy.
- Decomposition of KClO₃: 2KClO₃ → 2KCl + 3O₂, catalyst MnO₂.
- Haber's process: N₂ + 3H₂ → 2NH₃, catalyst Fe.
Negative catalysis
The catalyst (inhibitor) decreases the rate of the reaction.
- Decomposition of H₂O₂ is slowed by glycerol or acetanilide.
- Oxidation of sodium sulphite solution by air is slowed by alcohol.
| Point | Positive | Negative |
|---|---|---|
| Rate | Increased | Decreased |
| Activation energy | Lowered | Raised |
✓ Answer checked by Claude Opus 5.5 (high effort)
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