Paper: CSIR-NET June 2016 · Subject: Physical Chemistry · Chapter: Chemical Kinetics · Topic: Rate Laws Order · Marks: 2 · Difficulty: Medium
If experimentally observed rate constant is greater than the maximum value of rate constant obtained using hard-sphere model of collision theory, then relation between the impact parameter (b) and sum of the radii of two reactants is
(b)$\mathrm{b}<\mathrm{r}_{1}+\mathrm{r}_{2}$
(a)$b=r_{1}+r_{2}$
(c)$b>r_{1}+r_{2}$
(d)$b \leq r_{1}+r_{2}$
Answer
Answer: C ✓ checked by 4AB · confidence high
The source book printed no answer; this one was worked out and checked — see the explanation.
Explanation
k_obs > k_hard-sphere means the effective reaction cross-section exceeds π(r₁ + r₂)² — reaction occurs at impact parameters b > r₁ + r₂ (the harpoon mechanism).