$S{O}_2-S{O}_3-O_2$ mixtures

Exm: Calculate the composition of the gas mixture at equilibrium at $1000K$ if $1molofS{O}_2$ is reacted with $\frac{1}{2}$ moles of $O_2$

$S{O}_2+\frac{1}{2}{O}_{2}S{O}_3,G^0=-94600+89\mathrm{.}37TJ$