Entropy is a measure of randomess of system. When a liquid is converted to the vapour state entropy of the system increases. Entropy in the phase transformation is calculated using `Delta S = (Delta H)/(T)` but in reversible adiabatic process `Delta`S will be zero. The rise in temperature in isobaric or isochoric process increases the randomness of system, which is given by
`Delta S = "2.303 n C log"((T_(2))/(T_(1)))`
`C = C_(P) or C_(V)`
The temperature at whicgh liquid `H_(2)O`will be in equrilibrium with its vapour is (`Delta H and Delta S` for vapourisation are 50 kJ `mol^(-1)` and 0.15 kJ `mol^(-1)K^(-1)`)

Explanation

Given, `DeltaH = 40.00 kJ mol^(-1)`
`DeltaS = 0.100 kJ mol^(-1) K^(-1)` and `DeltaG =0`
Applying `DeltaG = DeltaH - T DeltaS`
`0 =40.00 - T xx 0.10`
`T = (40.00)/(0.109) = 400.0 K`