The numerical value of the activation energy for the reverse reaction is A - VCE - SSCE Chemistry - Question 3 - 2003 - Paper 1

To find the activation energy for the reverse reaction, one must consider the standard activation energy and the change in energy during the reaction. Activation energy is generally determined from the energy profile for a reaction.

If the forward reaction has an activation energy of, for instance, +100 kJ/mol, the activation energy for the reverse reaction can be found using the relationship:

$E_{a_{reverse}} = E_{reaction} + E_{a_{forward}}$

This means, if the reaction is exothermic (releases energy), then the activation energy for the reverse reaction will indeed be higher. By taking the options given: +150, +50, -50, and -100, we deduce:

If we assume the energy changes lead us to the conclusion that the most suitable numerical value among the choices would then be +150 kJ/mol, as it indicates the required activation energy for the products to convert back to reactants.