The energy equivalent of 0.5 g of a substance is:

Einstein's theory of special relativity gives the relation between mass and energy. 

Energy, $E=m{c}^2$, where $c$ is the speed of light.

$E=0.5\times {10}^{-3}\times 9\times {10}^{16}$

$\Rightarrow E=4.5\times {10}^{13} \mathrm{J}$