Question

Calculate the entropy change when 9g of water changes from liquid state to the vapour state at 100 and at a pressure of 1 atmosphere. The heat of vaporization of water is 540calg.

Answer 1

Latent Heat of water = 540 cal/g.

Heat required to vapourize 9g water

= m x L

= 9 x 540 cal

= 4860 cal or 

= 4860 x 4.18

= 20.3 KJ

∴ Change in entropy = \(\frac{20.3\times10^3}{373}\) J/K

= 54.4 J/K