\(\Delta \mathrm{U}=\mathrm{nC}_{\mathrm{V}}\left[\mathrm{T}_{2}-\mathrm{T}_{1}\right]\)
\(\Rightarrow \quad 5000=4 \times \mathrm{C}_{\mathrm{V}}[500-300]\)
\(\Rightarrow \quad \mathrm{C}_{\mathrm{v}}=\frac{5000}{800}=6.25 \mathrm{J}\) \(mole\) \(^{-1} \mathrm{K}^{-1}\)
$CCl _{4( g )} + 2 H _2 O ( g ) \rightarrow CO _{2( g )} + 4 HCl ( g )$