Question

When 1 gm of water changes from liquid to vapour phase at constant pressure of 1 atmosphere,
the volume increases from 1cc to 1671cc. The heat of vaporisation at this pressure is 540 cal/gm.
Increase in internal energy of water is (1 atmosphere =1.01 x 106 dyne/cm2)
(A) 4200J
(B) 8200J
(C) 1200J
(D) 2100 J​

Answer 1

Answer:

Change in Internal energy = Q in - work done 

It s a constant pressure work 

∴wD=P(V2−V1)    

=1.01×105[1.671−1]×10−6

=169.21s   

P=1atm

 =1.0.1×105Pa

=1.01×106cm2dyne

Latent heat of vaporization =540gmcal×(1gm)

=540cal

1cal=4.184J.

=540×4.184

=2259.36J

∴ΔU=2259.36−169.21

=2090Joules

≈2100Joules 

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