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Forward and backward activation energies and the reaction enthalpy

This type of question, asked 3 times: 2021 Paper 25, 15 Apr 2023, 4 Apr 2025. All 3 questions below, oldest first.

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  1. Question 1

    2021 Paper 25

    57
    An exothermic reaction X→YX \rightarrow Y has an activation energy 30 kJ mol−130\text{ }kJ{\text{ }mol}^{- 1}. If energy change ΔE\Delta E during the reaction is −20 kJ- 20\text{ }kJ, then the activation energy for the reverse reaction in kJkJ is

  2. Question 2

    15 Apr 2023

    58
    For a reversible reaction A⇌BA \rightleftharpoons B, the ΔHforward \Delta H_{\text{forward~}} reaction =20 kJ mol−1= 20\text{ }kJ{\text{ }mol}^{- 1}. The activation energy of the uncatalysed forward reaction is 300 kJ mol−1300\text{ }kJ{\text{ }mol}^{- 1}. When the reaction is catalysed keeping the reactant concentration same, the rate of the catalysed forward reaction at 27∘C27^{\circ}C is found to be same as that of the uncatalysed reaction at 327∘C327^{\circ}C. The activation energy of the catalysed backward reaction is___ kJmol−1kJmol^{- 1}.

  3. Question 3

    4 Apr 2025

    32
    For A2+B2⇌2ABA_{2}+B_{2}\rightleftharpoons 2AB EaE_{a} for forward and backward reaction are 180 and 200 kJ mol−1200\text{ }kJ{\text{ }mol}^{- 1} respectively If catalyst lowers EaE_{a} for both reaction by 100 kJ mol−1100\text{ }kJ{\text{ }mol}^{- 1}. Which of the following statement is correct?

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