Chemical Thermodynamics Question 348
Question: Assuming that water vapour is an ideal gas, the internal energy change $ ( \Delta U ) $ when 1 mol of water is vapourised at 1 bar pressure and $ 100{}^\circ C, $ (given : molar enthalpy of vapourisation of water at 1 bar and $ 373K=41kJmo{{l}^{-1}} $ and $ R=8.3,J,mo{{l}^{-1}}{{K}^{-1}} $ ) will be
Options:
A) $ 41.00kJ,mo{{l}^{-1}} $
B) $ 4.100kJ,mo{{l}^{-1}} $
C) $ 3.7904kJmo{{l}^{-1}} $
D) $ 37.904kJmo{{l}^{-1}} $
Show Answer
Answer:
Correct Answer: D
Solution:
- Given $ \Delta H=41kJmo{{l}^{-1}}=41000Jmo{{l}^{-1}} $
$ T=100{}^\circ C=273+100=373K $
$ \Delta n=1 $
$ \Delta U=\Delta H-\Delta nRT=41000-( 1\times 8.314\times 373 ) $
$ =37898.88,Jmo{{l}^{-1}}\simeq 37.9kJ,mo{{l}^{-1}} $
