b
Many enthalpy changes are difficult to measure directly under standard conditions. Hess law states that the total enthalpy change of a reaction is independent of the route taken. To find

\(H _{ f }, C _{( s )}+\frac{1}{2} O _{2}( g ) \rightarrow CO ( g )\)

Given:- combustion of carbon

\(C + O _{2} \rightarrow CO _{2}: \Delta H _{1}=-393.5 KJmol\)

combination of carbon monoxide

\(CO +\frac{1}{2} O _{2} \rightarrow CO _{2}: \Delta H _{2}=-283.5 kJ mol ^{-1}\)

Formation of carbon monoxide:

\(\triangle H =\triangle H _{1}-\Delta H _{2}=-393.5-(-283.5)\)

\(=39.3 .5+283.5=-110 kJ / mol\)