Q13 · CSIR-NET Chemistry, December 2011

Paper: CSIR-NET December 2011 · Subject: Physical Chemistry · Chapter: Chemical Kinetics · Topic: Chemical Kinetics – General · Marks: 2 · Difficulty: Medium

At any temperature for the following reaction (D and T are deuterium and tritium respectively) correct statement is:
\[ \text{(A) } \mathrm{HCl+F \rightarrow HF+Cl}, \quad \text{(B) } \mathrm{DCl+F \rightarrow DF+Cl} \quad \text{(C) } \mathrm{TCl+F \rightarrow TF+Cl} \]
(a)(A) is fastest
(b)(B) is fastest
(c)(C) is fastest
(d)All the above reactions have the same rate constant.
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
Breaking H–Cl is fastest: the heavier isotopes have lower zero-point energies, so the D–Cl and T–Cl bonds need more activation energy (primary kinetic isotope effect, k_H > k_D > k_T).

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