Activitation energy problem...

Question

It's been a while since I have worked these problems and think I got them all wrong on the test. I'm reviewing for a final tomorrow, please help!

Assume that the activation energy was measured for both the forward (Ea = 185kJ/mol) and reverse (Ea = 120 kJ/mol) directions of a reversible reaction. A catalyst decreases the activation energy for the forward reaction to 90kJ/mol. What would be the activation energy for the CATALYZED REVERSE reaction?

a. Ea = 25 kJ/mol

b. Ea = 30 kJ/mol

c. Ea = 95 kJ/mol

d. Ea = 155 kJ/mol

e. Ea = 215 kJ/mol

The answer is somehow a. Ea = 25 kJ/mol. Please tell me how to work this problem! Thank you!

Answer 1

You know that the activation energy of the forward reaction was originally 185 KJ/mol but with the catalyst it got lowered to 90 KJ/mol.

185-90=95 KJ/mol

So the catalyst decreases the activation energy of the forward reaction by 95 KJ/mol. The catalyst will also decrease the activation energy of the reverse reaction by the same amount, 95 KJ/mol.

So the if the activation energy of the reverse reaction was originally 120 KJ/mol and we decrease it by 95 KJ/mol we get 120-95=25 KJ/mol. So the activation energy of the reverse reaction is decreased to 25 KJ/mol.