Calcium carbide reacts with oxygen according to the reaction:

$2Ca{C}_2(s)+5O_2(g)2$CaO$(s)+4C{O}_2(g)$

A reaction mixture initially contains $5\mathrm{.}5mo{l}_{Ca{C}_2}$ and $15\mathrm{.}0mol{O}_2.$

What amount in moles of the excess reactant is left