\(\Delta n _{ g }=2-3=-1\)
\(\Delta_{ C } H =\Delta_{ c } U +\left(\Delta n _{ g }\right) RT\)
\(\Delta_{ c } H =\Delta_{ c } U - RT\)
\(\Delta_{ c } U =\Delta_{ c } H + RT\)
\(=-327 \times 10^{3}+2 \times 300\)
\(=-326400 cal\)
: Heat evolved
\(=326400 cal\)
$2Al + C{r_2}{O_3} \to A{l_2}{O_3} + 2Cr$