Given that `:`
`2CO_((g))+O_(2(g))rarr2CO_(2(g)),DeltaH^(@)=-P kJ`
`C_((s))+O_(2(g))rarr CO_(2(g)), DeltaH^(@)=-Q kJ`
the enthalpy of formation of carbon monoxide is `:`

Options

A. `(P-Q)/(2)`
B. `2Q-P`
C. `P-2Q`
D. `(P-2Q)/(2)`

Answer

D

Explanation

`2CO_((g))+O_(2(g))rarr2CO_(2(g)),DeltaH_(1)=-PkJ`
`C_((s))+O_(2(g))rarr CO_(2(g)),DeltaH_(2)=-QkJ`
`C_((s))+``^(1/2)O_(2(g))rarrCO_((g)),DeltaH_(3)=?`
`DeltaH_(3)=DeltaH_(2)-1//2DeltaH_(1)`
`=-Q-(-(P)/(2))=-Q+(P)/(2)`
`=(P-2Q)/(2)`