Assuming that water vapour is an ideal gas, the internal energy change `(DeltaU)` when 1 mole of water is vaporised at `1 ba r` pressure and` 100^(@)C, (` given`:` molar enthalpy of vaporization of water `41kJ mol^(-1)` at `1 ba r` and `373 K ` and `R=8.3 J mol^(-1)K^(-1))` will be `:`

Options

A. `41.00 kJ mol^(-1)`
B. `4.100 kJ mol^(-1)`
C. `3.7904 kJ mol^(-1)`
D. `37.904 kJ mol^(-1)`

Answer

D

Explanation

`underset(1"mol")(H_(2)O(l))tounderset(1"mol")(H_(2)O(g))`
`:. Deltan_(g)=1"mole"`
`DeltaH_(vap)=41k J mol^(-1)`
`:. DeltaU=DeltaH-Deltan_(g)RT`
`=41 kJ mol^(-1)-1xx8.3xx10^(3)kJ mol^(-1)xx373 cals`
`=(41-3.096)kJ mol^(-1)=37.904 kJ mol^(-1)`