# Inrease or decrease in entorpy?

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#1
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2CH3OH(l) + 3O2(g) --> 2CO2(g) + 4H2O(l)
I think entropy increases, but I'm wrong according to the markscheme, heres my logic and how i went about answering the question(does entropy inrease or decrease), perhaps you can find wheer I'm going wrong:

>So there are 2 moles of liquid on the LHS and 4 moles of liquid of the RHS. This means looking at this alone entorpy seems to increase, since there are more molecules of liquid and therefore disorder/random movement.

>Looking at the rest of the equation I can see that there are 3 moles of gas on the LHS but only 2 moles of gason the RHS. So looking at this part of the equation entropy has decreased.

>So now i look at it collectively and see that moles of liquid has increased from 2 --> 4 and moles of gas has decreased from 3 --> 2. In my mind the increase in moles of liquid outweighs that of the decrease in gaseous moles.

>Why am I wrong? What is the systematic method of tacking this question?

Any help will be appreciated

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3 years ago
#2
gases have more disorder than liquids and so they will have a much greater influence on the entropy of the system than liquids have
just by the number of moles decreasing by 1, that would outweigh any increase in entropy of the liquids
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#3
(Original post by lewisli_)
gases have more disorder than liquids and so they will have a much greater influence on the entropy of the system than liquids have
just by the number of moles decreasing by 1, that would outweigh any increase in entropy of the liquids
In that case how much decrease in moles of liquids would equate the decrease in entorpy caused by decreasing gasses by 1 mole in a system?
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3 years ago
#4
i wouldn’t be able to say as it depends for each equation but that’s the reason why this is a decrease in entropy
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3 years ago
#5
(Original post by Yme2day)
In that case how much decrease in moles of liquids would equate the decrease in entorpy caused by decreasing gasses by 1 mole in a system?
Just look up a few molar entropy values.

Water 70 JK-1 mol-1
Oxygen 205 JK-1 mol-1
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