Q.

A sample of 0.1 g of water at 100°C and normal pressure (1.013×105N m-2) requires 54 cal of heat energy to convert to steam at 100°C. If the volume of the steam produced is 167.1 cc, the change in internal energy of the sample is              [2018]
 

1 104.3 J  
2 208.7 J  
3 42.2 J  
4 84.5 J  

Ans.

(2)

Using first law of thermodynamics, ΔQ=ΔU+ΔW

  54×4.18=ΔU+1.013×105(167.1×10-6-0)

  ΔU=208.7J