The activation energy for the reaction no2(g)+co(g)⟶no(g)+co2(g) is ea = 100 kj/mol and the change in enthalpy for the reaction is δh = -250 kj/mol . what is the activation energy for the reverse reaction?

350 kJ/mol

Explanation:

1) δh = -250 kj/mol means that the products of the forward reaction are 250 kJ/mol lower in the potential enery diagram.

2) So, the reverse reaction must compensate the 250 kJ/mol and go upper as much as the activation energy of the forward reaction.

This is: Ea reverse = Ea forward + | δh |

You can see this clearer on the attached graph of an exothermic reaction.

Ea reverse = 100 kJ / mol + | -250 kJ/mol | = 100 kJ/mol + 250 kJ/mol = 350 kJ/mol