Chemical Thermodynamics Question 372
Question: The $ ( S{}^\circ ) $ of the following substances are:
$ CH_4( g )186.2J{{K}^{-1}}mo{{l}^{-1}} $
$ O_2( g )205.2J{{K}^{-1}}mo{{l}^{-1}} $
$ CO_2( g )213.6J{{K}^{-1}}mo{{l}^{-1}} $
$ H_2O( g )69.9.J{{K}^{-1}}mo{{l}^{-1}} $
The entropy change $ ( \Delta {{S}^{{}^\circ }} ) $ for the reaction $ CH_4(g)+2O_2(g)\to CO_2(g)+2H_2O(l) $ is:
Options:
A) $ -312.5J,{{K}^{-1}}mo{{l}^{-1}} $
B) $ -242.8J,{{K}^{-1}},mo{{l}^{-1}} $
C) $ -108.1J,{{K}^{-1}},mo{{l}^{-1}} $
D) $ -37.6J{{K}^{-1}}mo{{l}^{-1}} $
Show Answer
Answer:
Correct Answer: B
Solution:
- $ \Delta S{}^\circ =S{{{}^\circ } _{CO_2}}+2\times S{{{}^\circ } _{H_2O}}-(S{{{}^\circ } _{CH_4}}+2\times S{{{}^\circ } _{O_2}}) $
$ =( 213.6+2\times 69.9 )-( 186.2+2\times 205.2 ) $
$ =-242.8J{{K}^{-1}},mo{{l}^{-1}}. $
