Assuming that water vapour is an ideal gas, the internal energy change `(DeltaU)` when 1 mole of water is vaporised at 1 bar pressure and `100^(@)C` , (given: molar enthalpy of vaporisation of water `-41KJmol^(-1)` at 1 bar and `373K` and `R=8.3Jmol^(-1)Kmol^(-1)`) will be:

Options

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

Answer

C

Explanation

`H_(2)O_((l))overset(vap o risation)(rarr)H_(2)O_((g))`
`Deltan_(g)=1-0=1`
`DeltaH=DeltaU+Deltah_(g)RT`
`DeltaU=DeltaH-Deltan_(g)RT`
`=41-8.3xx10^(-3)xx373=37.9KJmol^(-1)`