Question

Reaction, $A+B⟶C+D+38kcal$ has activation energy $20kcal$. Activation energy for the reaction, $C+D⟶A+B$ is:

• A. $20kcal$
• B. $-20kcal$
• C. $18kcal$
• D. $58kcal$

Answer 1

The correct option is D $58kcal$

Reaction, $A+B⟶C+D+\text{38 kcal}$ has activation energy $\text{20 kcal}$. Activation energy for the reaction, $C+D⟶A+B$ is $20\text{kcal}+38\text{kcal}=58\text{kcal}$.
Note:
The reaction is exothermic as for exothermic reaction (heat liberated during reaction),
$E_{a,r}=E_{a,f}+\Delta H_{rxn}$
$E_{a,f}=$ activation energy for forward reaction
$E_{a,r}=$ activation energy for reverse reaction
$\Delta H_{rxn}=$ enthalpy change for the reaction.