entropy of irreversible and reversible reactions.

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Ekayana Sethi 2K
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entropy of irreversible and reversible reactions.

Postby Ekayana Sethi 2K » Sat Feb 10, 2018 11:33 am

Are the entropies of irreversible and reversible reactions the same? how are they related?

Remi Lathrop 1G
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Joined: Fri Sep 29, 2017 7:07 am

Re: entropy of irreversible and reversible reactions.

Postby Remi Lathrop 1G » Sat Feb 10, 2018 12:13 pm

For a reversible reaction, the key is that the ∆S(total) is equal to 0. Because ∆S + ∆S (surroundings) = ∆S (total), when ∆S (total) is 0, this means that ∆S and ∆S (surroundings) have opposite signs.

For example, if ∆S = 0.15 J/K for a reversible reaction, then ∆S (surroundings) must be equal to -0.15 J/K because together they have to add to 0.

An irreversible reaction is similar, but not the same. The ∆S will be the same in both cases, but for an irreversible reaction the ∆S (surroundings) will be 0 if your system is free expansion because there will be no outside force pushing on the reaction. Therefore ∆S + 0 = ∆S (total), so ∆S and ∆S (total) will have the same sign.

Helen Shi 1J
Posts: 78
Joined: Sat Jul 22, 2017 3:00 am

Re: entropy of irreversible and reversible reactions.

Postby Helen Shi 1J » Sat Feb 10, 2018 1:07 pm

I don't understand why the delta S of the surroundings is zero in an irreversible process. The textbook on page 346 says that no work is done in free expansion so w=0. Can someone explain that?


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