What is the enthalpy for the following reaction? overall: C + 12O2→CO?
As a practical matter pisgahchemist is correct.
However, supposing you meant:
C + ½ O2 → CO
your equation illustrates the standard enthalpy of formation of CO, which the source
below lists as −110.525 kJ/mol.
You meant to write this:
C(s) + ½O2(g) –> CO(g)
Burning carbon in oxygen produces carbon dioxide gas when the combustion is complete. Otherwise there will be a mixture of CO2 and CO. There is no reaction where CO is the single product.