Question

Given the following diagram for the reaction $A+B\to C+D$. The enthalpy change and activation energy for the reverse reaction $C+D\to A+B$ respectively, are :

• A. x, y
• B. x, x+y
• C. y, x+y
• D. y, y+z

Answer 1

Answer: (C)

y, x+y

The enthalpy change for the backward reaction is equal in magnitude and opposite in sign to that for the forward reaction.
Thus the magnitude of the enthalpy change for the backward reaction is $y$.
The activation energy for the backward reaction is equal to the sum of the activation energy of the forward reaction and the enthalpy change of the reaction.
It is equal to $x+y$.