$$ \underset{(\mathrm{l})}{\mathrm{C}_7 \mathrm{H}_{16}}+\underset{(\mathrm{g})}{11 \mathrm{O}_2} \xrightarrow{\Delta} \underset{(\mathrm{~g})}{\mathrm{CO}_2}+\underset{(\mathrm{l})}{8 \mathrm{H}_2 \mathrm{O}} $$ $$ \Delta \mathrm{H}-\Delta \mathrm{U}=\Delta \mathrm{n}_{\mathrm{g}} \mathrm{RT} $$ $$ \because \quad \Delta \mathrm{n}_{\mathrm{g}}=-4 $$ $$ \therefore \quad \Delta \mathrm{H}-\Delta \mathrm{U}=-4 \mathrm{RT} $$