Q126 / 200 · MHT CET - Medical 2026 (21 April Shift 2) · Chemistry
Which of the following statements is NOT true about the decomposition of ammonia on platinum metal?
- AThe rate of reaction is independent of the concentration of ammonia
- BUnit of rate constant is the unit of rate of reaction
- Correct answerCHalf life period of reaction is independent of the initial concentration of ammonia
- DOrder of reaction is zero
Solution
The decomposition of ammonia gas on a hot platinum surface is a zero-order reaction at high pressure.
For a zero-order reaction, the rate law is given by Rate = $k[\text{NH}_3]^0 = k$.
Since the rate is equal to the rate constant $k$, the rate of reaction is independent of the concentration of ammonia, and the unit of the rate constant is the same as the unit of the rate of reaction.
The half-life period for a zero-order reaction is given by $t_{1/2} = \dfrac{[\text{A}]_0}{2k}$.
Thus, the half-life period is directly proportional to the initial concentration of ammonia, not independent of it.
Therefore, the statement that the half-life period is independent of the initial concentration is incorrect.
Answer: Half life period of reaction is independent of the initial concentration of ammonia
For a zero-order reaction, the rate law is given by Rate = $k[\text{NH}_3]^0 = k$.
Since the rate is equal to the rate constant $k$, the rate of reaction is independent of the concentration of ammonia, and the unit of the rate constant is the same as the unit of the rate of reaction.
The half-life period for a zero-order reaction is given by $t_{1/2} = \dfrac{[\text{A}]_0}{2k}$.
Thus, the half-life period is directly proportional to the initial concentration of ammonia, not independent of it.
Therefore, the statement that the half-life period is independent of the initial concentration is incorrect.
Answer: Half life period of reaction is independent of the initial concentration of ammonia
Hence, the correct answer is option: 'C'.