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}} $

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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}} $



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