## Predict entropy change

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

Lorena Zhang 4E
Posts: 63
Joined: Fri Sep 28, 2018 12:16 am

### Predict entropy change

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?

Anushi Patel 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:19 am
Been upvoted: 1 time

### Re: Predict entropy change

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.

amogha_koka3I
Posts: 62
Joined: Fri Sep 28, 2018 12:24 am

### Re: Predict entropy change

So we look only at gas moles and not at the changes in the other phase moles?

Sophie Roberts 1E
Posts: 61
Joined: Fri Sep 28, 2018 12:17 am

### Re: Predict entropy change

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.