Assuming that water vapour is an ideal gas, the internal energy change `(Delta U)` when `1 mol` of water is vapourised at `1` bar pressure and `100^(@)C`, (Given: Molar enthalpy of vapourization of water at `1` bar and `373K=41 kJ mol^(-1)` and `R=8.3J mol^(-1)K^(-1)`) will be:

Options

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

Answer

C

Explanation

`H_(2) O_((l)) overset("vapourisation") rarr H_(2)O_((g))`
`Delta n_(g)=1-0=1`
`Delta H=Delta U + Delta n_(g) RT`
`Delta U = Delta H- Delta n_(g)RT`
`=41-8.3xx10^(-3) xx373 =37.9 kJ mol^(-1)`