Question

Standard molar enthalpy of formation of $C{O}_2$ is equal to:

• A. zero
• B. the standard molar enthalpy of combustion of gaseous carbon
• C. the sum of standard molar enthalpies of formation of $CO$ and $O_2$
• D. the standard molar enthalpy of combustion of carbon (graphite)

Answer 1

The correct option is D the standard molar enthalpy of combustion of carbon (graphite)

Standard molar heat enthalpy $\left(H^{\circ }\right)$ of a compound is equal to its standard heat of formation from most stable states of initial components.
Hence, standard molar enthalpy of formation of $C{O}_2$ is equal to the standard molar enthalpy of combustion of carbon (graphite).
$C\left(g\right)+O_2\left(g\right)\to C{O}_2\left(g\right)$
The above reaction can be regarded as the reaction for the combustion of carbon (graphite).
Same reaction can also be regarded as the reaction for the formation of carbon dioxide.