Question

Choose the correct set of reactions which follow first order kinetics:
(i) Thermal decomposition of HI on gold surface.
(ii) Thermal decomposition of $N_2O_5(g)$ at constant volume.
(iii) Hydrogenation of ethene.
(iv) Decomposition of $NH_3$ on a hot Pt surface.
(v) Thermal decomposition of $SO_2Cl_2(g)$ at constant volume.

• A. i, ii, iii
• B. i, iii, iv
• C. i, iv, v
• D. ii, iv, v
• E. ii, iii, v

Answer 1

The Correct Option is D

Choose the correct set of reactions which follow first order kinetics:

1. Thermal decomposition of HI on gold surface.
2. Thermal decomposition of \( N_2O_5(g) \) at constant volume. 
3. Hydrogenation of ethene.
4. Decomposition of \( NH_3 \) on a hot Pt surface.
5. Thermal decomposition of \( SO_2Cl_2(g) \) at constant volume.

Correct Answer: ii, iv, v

Explanation:

• (ii) \( N_2O_5 \) decomposition is a classic first-order reaction.
• (iv) Decomposition of ammonia on hot platinum follows first-order kinetics at low pressure (surface catalyzed reaction).
• (v) \( SO_2Cl_2 \) decomposition is known to be a first-order reaction.

Incorrect Options:

• (i) HI decomposition on gold surface does not strictly follow first-order kinetics—it depends on the surface and conditions.
• (iii) Hydrogenation of ethene is typically a surface reaction and doesn't show simple first-order behavior.