![Q.10 For a reaction A + B → products, the following data was obtained: [A] (M) [B] (M) Initial rate 0.1 0.1 r 0.2 0.1 4r [A]₀ and [B]₀ are initial concentrations of A and B respectively. The overall order of the reaction is (A) 2 (B) 3 (C) 4 (D) 6](https://www.letstalkacademy.com/wp-content/uploads/2026/01/slide_90png.png)
Q.10 For a reaction A + B → products, the following data was obtained:
| [A] (M) | [B] (M) | Initial rate |
|---|---|---|
| 0.1 | 0.1 | r |
| 0.2 | 0.1 | 4r |
[A]₀ and [B]₀ are initial concentrations of A and B respectively.
The overall order of the reaction is
(A) 2
(B) 3
(C) 4
(D) 6
Overall Order of Reaction A + B → Products from Initial Rate Data
Rate Data Analysis
Experimental data shows three trials:
- [A] = 0.1 M, [B] = 0.1 M, rate = r (trial 1)
- [A] = 0.1 M, [B] = 0.2 M, rate = 4r (trial 2)
- [A] = 0.2 M, [B] = 0.1 M, rate = 2r (trial 3)
Assume rate law: rate = k [A]x [B]y.
Doubling [B] from trial 1 to 2 (while [A] is constant) increases the rate by a factor of 4, so:
(2)y = 4 → y = 2
Doubling [A] from trial 1 to 3 (while [B] is constant) increases the rate by a factor of 2, so:
(2)x = 2 → x = 1
Option Breakdown
Options:
- (A) 2 — Fails, as orders sum to 3, not matching rate quadrupling on [B] double (expects double for first order).
- (B) 3 — Correct, overall order x + y = 1 + 2.
- (C) 4 — Mismatches data, as second order in both predicts 4-fold rate increase when doubling [A].
- (D) 6 — Excessive, implying higher orders unsupported by ratios.
CSIR NET Relevance
This initial rate method is key for CSIR NET Life Sciences kinetics questions, testing rate law derivation without integration. The rate law applies as:
rate = k [A]1 [B]2, with k calculable as:
k = r / (0.1 × 0.12)
Practicing such problems helps identify pseudo-order scenarios for exams.
