The activation energy for the reaction NO2 (g) + CO (g) ⟶NO (g) + CO2 (g) is Ea = 75 kJ/mol and the change in enthalpy for the reaction is ΔH = - 175 kJ/mol. What is the activation energy for the reverse reaction?

= 100kJ

Explanation:

The reverse reaction's activation energy of a reaction is the activation energy of the forward reaction plus ΔH of the reaction:

Ea of forward reaction = 75kJ

∆H = - 175 kJ/mol

Ea of reverse reaction = 75 + (-175)

= 100kJ

Note that a reverse reaction is one which can proceed in both direction depending on the conditions.