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)

If Δngas > 0, the entropy increases If Δngas < 0, the entropy decreases. If Δngas = 0, there is little or no change in the entropy.

Let's consider the following reaction.

2 H₂ (g) + O₂ (g) ⟶ 2 H₂O (l)

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