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

Answer 1

Answer: (B)

-110.5 kJ

Answer 2

(i) $C + O_2 \rightarrow CO_2; \Delta H = -393.5 \, kJ$ (ii) $CO + \frac{1}{2} O_2 \rightarrow CO_2; \Delta H = -283 \, kJ$ $C + \frac{1}{2} O_2 \rightarrow CO; \Delta H$ = ? Solve (i) - (ii), $\Delta$H = (-393.5)-(-283) kJ = (-393.5 + 283) kJ = -110.5 kJ.