The change in entropy, δ s ∘ rxn , is related to the the change in the number of moles of gas molecules, δ n gas . determine the change in the moles of gas for each of the reactions and decide if the entropy increases, decreases, or has little or no change. a. 2 h 2 ( g ) + o 2 ( g ) ⟶ 2 h 2 o ( l )

The entropy decreases.

Explanation:

The change in the standard entropy of a reaction (ΔS°rxn) is related to the change in the number of gaseous moles (Δngas), where

Δngas = n(gaseous products) - n(gaseous reactants)

Let's consider the following reaction.

2 H₂(g) + O₂(g) ⟶ 2 H₂O(l)

Δngas = 0 - 3 = -3, so the entropy decreases.