Thermodynamics

Thermodynamics

Question

The heats of combustion of carbon and carbon monoxide are −393.5 and −283.5 kJ mol−1, respectively. The heat of formation (in kJ) of carbon monoxide per mole is:

  • 676.5

  • -676.5

  • -110.5

  • 110 s

Answer

C.

-110.5

C(s) + O2 (g) → CO2 (g); ΔH = -393.5 kJ mol-1 ... (i)
CO + O2/2 → CO2 (g); ΔH = - 283.5 kJ mol-1 ....(ii)
On subtracting Eq. (ii) from Eq. (i), we get
C (s) + O2/2 (g) → CO (g)

ΔH = (-393.5 + 283.5) kJ mol-1 = - -110 kJ mol-1

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