Moles of gas formed & entropy change

[Olivia Fong 2k]

Hi! Are the change in moles of gas always an accurate predictor of the entropy change of a reaction? That is, if a reaction has a net increase in moles of gas, can we conclude that the entropy increases (delta S is positive) and vice versa? Thanks!

[405993361]

The change in moles is not always an accurate predictor of the entropy change. Phase changes can have high entropy changes even if the number of moles of gas does not change.

[Samantha Hernandez 2B]

The moles of gas can be an indicator of an increase in entropy, but it is more of an estimate than an exact answer. For example, textbook problem 4H.7(a):
Cl2(g) + H2O(l) --> HCl(aq) + HClO(aq)
depicts a decrease in entropy because the moles of gas are greater on the reactant side rather than the product.