For water $\Delta$_vap H = 41 kJ mol^$-$1 at 373 K and 1 bar pressure. Assuming that water vapour is an ideal gas that occupies a much larger volume than liquid water, the internal energy change during evaporation of water is ___________ kJ mol^$-$1

[Use : R = 8.3 J mol^$-$1 K^$-$1]