Question

Calculate the entropy change when `3.6g` of liquid water is completely converted into vapour at `100^(@)C` . The molar heat of vaporization is `40.85KJ mol^(-1)` .
A. `6.08JK^(-1)`
B. `109.5JK^(-1)`
C. `21.89JK^(-1)`
D. `-21.89JK^(-1)`

Answer 1

Correct Answer - C
`DeltaH_(vap)=40850Jmol^(-1),T_(b)=373K`
`DeltaS_("vap")=(DeltaH_("vap"))/(T_(b))=(40850Jmol^(-1))/(373K)=109.5K^(-1)mol^(-1)`
`DeltaS_(vap)` per gram `=(109.5JK^(-1)mol^(-1))/(18gmol^(-1))=6.-083JK^(-1)g^(-1)`
Entropy change for `3.6g` water `=6.083JK^(-1)g^(-1)xx3.6g`
`=21.89JK^(-1)`