Chemical Kinetics - Result Question 55
####56. The activation energy for a simple chemical reaction $A \to B$ is $E_a$ in forward direction. The activation energy for reverse reaction
[2003]
(a) Is always double of $E_a$
(b) Is negative of $E_a$
(c) Is always less than $E_a$
(d) Can be less than or more than $E_a$
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Solution:
- (d) The activation energy of reverse reaction will depend upon whether the forward reaction is exothermic or endothermic.
As $\Delta H=E _{a \text{ (forward reaction) }}-E _{a \text{ (backward reaction) }}$ For exothermic reaction
$\Delta H=-ve$
$\therefore-\Delta H=E _{a(f)}-E _{a(b)}$
or $E _{a(f)}=E _{a(b)}-\Delta H$
$\therefore E _{a(f)}<E _{a(b)}$
for endothermic reaction
$\Delta H=+ve$
$\therefore \Delta H=E _{a(f)}-E _{a(b)}$ or $E _{a(f)}=\Delta H+E _{a(b)}$
$\therefore E _{a(f)}>E _{a(b)}$.
