The enthalpy of formation of methane at constant pressure and `300 K` is `-75.83 kJ`. What will be the heat of formation at constant volume? `[R = 8.3 J K^(-1) mol^(-1)]`

Explanation

The equation for the formation of methane is
`C(s)+underset("2 moles")(2H_(2)(g))=underset("1 mole")(CH_(4)(g)),DeltaH=-75.83kJ`
`Deltan=(1-2)=-1`
Given `DeltaH=-75.83kJ,R=8.3xx10^(-3)kJ" "K^(-1)mol^(-1),T=300K`
Applying `DeltaH=DeltaU+DeltanRT`
`-75.83=DeltaU+(-1)(8.3xx10^(-3))(300)`
So, `DeltaU=-75.83+2.49`
`=-73.34kJ`