Question

What is the standard enthalpy of formation of carbon dioxide (CO2) given that the standard enthalpy of combustion of carbon (C) and hydrogen gas (H2) are -394 kJ/mol and -286 kJ/mol, respectively?

Answer 1

The standard enthalpy of formation of carbon dioxide  CO2  can be determined using the given information about the standard enthalpy of combustion of carbon  C  and hydrogen gas  H2 . The combustion reaction for carbon is:C  s  + O2  g   CO2  g The combustion reaction for hydrogen is:H2  g  + 1/2 O2  g   H2O  l However, we need to find the standard enthalpy of formation of CO2, which is the reaction:C  s  + O2  g   CO2  g Since the combustion reaction of carbon is the same as the formation reaction of CO2, the standard enthalpy of formation of CO2 is equal to the standard enthalpy of combustion of carbon.Therefore, the standard enthalpy of formation of CO2 is -394 kJ/mol.