For the formation of $\mathrm{HCl},$   
 

If the heat of combustion of carbon monoxide at constant volume and at $17 °\mathrm{C}$ is $–283.3 \mathrm{kJ},$ its heat of combustion at constant pressure is:
${\text{(R=8.314 J degree}}^{\text{-1}}{\text{ mol}}^{\text{-1}}\text{)}$

Enthalpy of combustion of ${\mathrm{C}}_6{{\mathrm{H}}_6}_{ \left(\mathrm{l}\right)}$at $298 \mathrm{K}$ to yield ${\mathrm{CO}}_{2 \left(\mathrm{g}\right)}$ and ${\mathrm{H}}_2{\mathrm{O}}_{ \left(\mathrm{l}\right)}$is $∆\mathrm{H} = –781.1 \mathrm{kcal}.$ Calculate $∆\mathrm{U}.$    

Which among the following thermochemical equations represent the formation of sodium chloride?

Enthalpy of formation of two compounds $\mathrm{x}$ and $\mathrm{y}$ are $\text{-84 kJ and -156 kJ}$, respectively. Which of the following statements is CORRECT?