The slope in Arrhenius plot, is equal to: 

Arrhenius equation is given by 

$\mathrm{k}={\mathrm{Ae}}^{-{\mathrm{E}}_{\mathrm{a}}/(2.303\mathrm{RT})}$

Taking log on both sides, we get 
$\log \mathrm{k}=\log \mathrm{A}-\frac{{\mathrm{E}}_{\mathrm{a}}}{2.303\mathrm{RT}}$
Arrhenius plot a graph between log k and  $\frac{1}{T}$whose 
slope is $\frac{-{\mathrm{E}}_{\mathrm{a}}}{2.303\mathrm{R}}$