What is the Ea for the reverse reaction in kJ/mol?

Question

For the reaction A B, the activation energy is Ea = 125 kJ/mol and the heat of reaction, H = 50. kJ/mol. What is the Ea for the reverse reaction in kJ/mol?

Answer 1

You have the reaction A->B
You say that ΔΗ =+50 kJ/mol. Thus the product is at a higher energy level.
So Ea(rev)= 125-50 =75 kJ/mol

Look at the figure



.. .. .. .. *
.. .. .. .. l .. .. .. .. .. .. .. ..l
.. .. .. .. l .. .. .. .. .. .. .. ..l Ea(rev)
.. .. .. .. l .. .. .. ..B __ .. l
.. .. .. .. l Ea.. ... l
.. .. .. .. l .. .. .. .. l ΔΗ
.. . ___A .. .. .. ..l

* denotes the peak in the graph (transition state)
horizontal line the energy level
vertical line the size of the respective energy (Ea the first column of vertical lines, ΔΗ the second, Ea(rev) the third)

Answer 2

50 + 125!