Question

standard enthalpy of vapourisation delta H for water at 100c is 40.66kj per mol.the internal energy of vapourisation of water at 100c? [in kj per mol] is

Answer 1

If there is no air drag then maximum height,                

H=u^2/2g=14×14/2×9.8=10m

But due to air drag ball reaches up to height 8m only.

So, loss in energy                 

=mg(10−8)

=0.5×9.8×2=9.8J

Answer 2

∆H=∆E+P∆V

Vf>Vi. when water convert into vapour from liquid

so. ∆H>∆E