Question

The enthalpies of combustion of carbon and carbon monoxide are $ -393.5$ and $ -283\,kJ\, mol^{-1}$ respectively. The enthalpy of formation of carbon monoxide per mole is

• A. -676.9 kJ
• B. 676.5 kJ
• C. 110.5 kJ
• D. -110.5 kJ

Answer 1

Answer: (D)

$C (s)+ O _{2}(g) \longrightarrow CO _{2}(g)$
$\Delta H=-393.5\, kJmol ^{-1}$
$CO (g)+\frac{1}{2} O _{2}(g) \rightarrow CO _{2}(g)$
$\Delta H=-283\, kJmol ^{-1}$
On subtracting equation (ii) from equation (i), we get
$C (s)+ O _{2}(g) \rightarrow CO (g) ; \Delta H=-110.5\, kJmol ^{-1}$
The enthalpy of formation of carbon monoxide
per mole $=-110.5\, kJmol ^{-1}$