Thermodynamics Question 227
Question: Unit mass of a liquid with volume $ V _{1} $ is completely changed into a gas of volume K, at a constant external pressure P and temperature T. If the latent heat of evaporation for the given mass is L, then the increase in the internal energy of the system is
Options:
A) Zero
B) $ P( V _{2}-V _{1} ) $
C) $ L-P( V _{2}-V _{1} ) $
D) $ L $
Show Answer
Answer:
Correct Answer: C
Solution:
[c] $ Q=mL=1\times L=L;W=P(V _{1}-V _{2}) $
Now $ Q=\Delta U+W $
$ \text{or }L=\Delta U+P( V _{2}-V _{1} ) $
$ \therefore \Delta U=L-P( V _{2}-V _{1} ) $
