Consider the following information for the reaction A + B → C - VCE - SSCE Chemistry - Question 18 - 2006 - Paper 1

To calculate the activation energy for the reverse reaction (C → A + B), we can use the relationship between the activation energy of the forward reaction and the heat of reaction:

$E_{a,reverse} = E_{a,forward} - ext{heat of reaction}$

Substituting the provided values:

$E_{a,reverse} = 200 ext{ kJ mol}^{-1} - (-120 ext{ kJ mol}^{-1})$

This simplifies to:

$E_{a,reverse} = 200 ext{ kJ mol}^{-1} + 120 ext{ kJ mol}^{-1}$

Calculating this gives:

$E_{a,reverse} = 320 ext{ kJ mol}^{-1}$

Thus, the correct answer is D. +320.