Question

Given below are two statements
Assertion (A) : Protium and deuterium differ in their rates of reactions
Reason (R) : They have different enthalpies of bond dissociation The correct answer is

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is incorrect
• D. (A) is incorrect but (R) is correct

Hint:

The kinetic isotope effect arises from the mass difference between isotopes, affecting bond strengths and reaction rates.

Answer 1

The Correct Option is A

Assertion (A): Protium and deuterium differ in their rates of reactions.

Reason (R): They have different enthalpies of bond dissociation.

To determine whether the assertion and the reason are correct and if the reason is the correct explanation for the assertion, we must examine each statement:

1. Understanding Isotopes: Protium and deuterium are isotopes of hydrogen. Protium has 1 proton and 0 neutrons, whereas deuterium has 1 proton and 1 neutron.

2. Rate of Reaction Difference: Isotopes differ in reaction rates due to the isotope effect, which is influenced by mass differences. Deuterium, being heavier than protium, generally reacts more slowly.

3. Bond Dissociation Enthalpy: The energy required to break a bond differs between isotopes due to mass differences, affecting the enthalpy of bond dissociation.

4. Link between Bond Enthalpy and Reaction Rate: The different bond dissociation enthalpies of protium and deuterium alter their reaction mechanisms and reaction rates.

Based on these reasons, both the assertion and reason are correct, and the different bond dissociation enthalpies explain why protium and deuterium react at different rates.

Conclusion: Both (A) and (R) are correct, and (R) is the correct explanation of (A).