Q.

1 kg of water at 100°C is converted into steam at 100°C by boiling at atmospheric pressure. The volume of water changes from 1.00×10-3m3 as a liquid to 1.671 m3 as steam. The change in internal energy of the system during the process will be (Given latent heat of vaporisation =2257 kJ/kg, atmospheric pressure =1×105 Pa)         [2023]

1 + 2090 kJ  
2 - 2090 kJ  
3 - 2426 kJ  
4 + 2476 kJ  

Ans.

(1)

ΔQ=ΔU+ΔW

  ΔU=ΔQ-ΔW=mLv-PΔV

                =(1 kg)(2257×103J/kg)

-(1×105 Pa)(1.671 m3-1×10-3 m3)

           =2257×103 J-167×103 J=2090 kJ