Question

At 17 degree Celsius the enthalpy of combustion of graphite to CO2 is - 23110 J and that of CO to CO2 is - 16261 J determine the enthalpy formation of CO at 17 degree celsius

Answer 1

enthalpy of combustion of graphite to carbon dioxide is -23110 J,
e.g., C + O2 ------> CO2 , ∆H1 = -23110 J -----(1)

enthalpy of combustion of Carbon monoxide to carbon dioxide is -16261J
e.g., CO + (1/2)O2 -------> CO2 , ∆H2 = -16261J -----(2)

now, we have to determine enthalpy of formation of CO,
e.g., we have to find out ,
C + 1/2O2 -----> CO , ∆H3 = ?

reverse the equation (2) and add it with equation (1)
CO2 -------> CO + 1/2O2 , -∆H2 = 16261J
C + O2 ------> CO2 , ∆H1 = - 23110J
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C + 1/2O2 ----> CO2 , ∆H3 = ∆H1 - ∆H2
∆H3 = -23110 + 16261 =- 6849 J

Hence, enthalpy of formation of CO is -6849 J