Question

$I$. $E_a=15$ $kJ$ ${mol}^{-1};$ $\Delta H=-70$ $kJ$ ${mol}^{-1}$
$II$. $E_a=30$ $kJ$ ${mol}^{-1};$ $\Delta H=-15$ $kJ$ ${mol}^{-1}$
$III$. $E_a=60$ $kJ$ ${mol}^{-1};$ $\Delta H=+20$ $kJ$ ${mol}^{-1}$
If above reactions are at same frequency factor and temperature, then fastest and slowest reactions are:

• A. $III$ is faster, $II$ is slowest
• B. $I$ is faster, $III$ is slowest
• C. $II$ is faster, $III$ is slowest
• D. $III$ is faster, $I$ is slowest

Answer 1

Answer: (B)

$I$ is faster, $III$ is slowest

$k=A{e}^{-\frac{E_a}{RT}}$

Higher the value of $E_a$, lower is the k value or slower is the reaction.

I will be fastest while III will be slowest