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Predict entropy change

Posted: Sat Feb 09, 2019 9:41 am
by Lorena Zhang 4E
Without performing any calculations, predict whether there is an increase or a decrease in entropy for each of the following processes:
(a) Cl2 (g) + H2O (l) --> HCl (aq) + HClO (aq)

The answer says that entropy decreases because there's not as many moles of gas on the right side of the equation. Does gas always take priority when predicting the entropy change? What if there are significantly more moles of aqueous/liquid on the product side(but without gas) and the reactant side has few moles of gas and solids, would the answer still be decrease?

Re: Predict entropy change

Posted: Sat Feb 09, 2019 9:58 am
by Anushi Patel 1J
From what I know, the difference in entropy between a gas and a liquid is greater than the difference in entropy between a liquid and a solid. Since gas molecules have many more possible positions than molecules in the liquid state, it's safe to say that gases take precedence.

Re: Predict entropy change

Posted: Sat Feb 09, 2019 10:41 am
by amogha_koka3I
So we look only at gas moles and not at the changes in the other phase moles?

Re: Predict entropy change

Posted: Sun Feb 10, 2019 3:31 pm
by Sophie Roberts 1E
Gases have greater entropy, because gas molecules expand to fill their whole container and can move around freely so there is more disorder... So since this reaction goes from having one mole of gas to having zero, its entropy decreases.