The ethalpy 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)+,2H_(2)(g)rarr,CH_(4)(g),DeltaH^(Theta) =- 67.83kJ,,),(,2mol,1mol,,):}`
`Deltan = (1-2) =- 1`
Given `DeltaH^(Theta) =- 75.83 kJ R = 8.3 xx 10^(-3) kJ K^(-1) mol^(-1), T = 300 K`
Applying `DeltaH^(Theta) = DeltaU^(Theta) + DeltanRT`
`- 75.83 = DeltaU^(Theta) +(-1) (8.3 xx 10^(-3)) (300)`
So, `DeltaU^(Theta) =- 75.83 + 2.49 =- 73.34 kJ`