ENTROPY AND FREE ENERGY Qualitatively predicting reaction entropy Note fo nced students: Assume the temperature remains constant: Assume all g= reaction sign of reaction entropy As rxn colg) + 2Hz (g) CH,OH (g) not enough information_ ASrxn ASrn 250,(g) 250,( (g) + 02 (g) not enough information_ 4s rxn *4,so,() K,o() H,o’ (a9) HSO4 (aq) 4s Txn not enough Information ASrxn
The Correct Answer and Explanation is:
Correct Answers:
- CO(g) + 2H₂(g) → CH₃OH(g)
✔ ΔSᵣₓₙ < 0 - 2SO₃(g) → 2SO₂(g) + O₂(g)
✔ ΔSᵣₓₙ > 0 - H₂SO₄(l) + H₂O(l) → H₃O⁺(aq) + HSO₄⁻(aq)
✔ ΔSᵣₓₙ > 0
Explanation:
Entropy (S) is a measure of disorder or randomness in a system. In chemical reactions, entropy changes (ΔSᵣₓₙ) can be predicted qualitatively based on the physical states and number of particles involved.
1. CO(g) + 2H₂(g) → CH₃OH(g)
This reaction goes from 3 moles of gas (1 CO + 2 H₂) to 1 mole of gas (CH₃OH). The number of gas particles decreases, resulting in a decrease in entropy. Gases have high entropy, and fewer gas particles mean lower disorder.
✔ ΔSᵣₓₙ < 0
2. 2SO₃(g) → 2SO₂(g) + O₂(g)
This process results in more gas particles: 2 reactant gas molecules become 3 product gas molecules (2 SO₂ + 1 O₂). The increase in gas molecules means greater randomness and increased entropy.
✔ ΔSᵣₓₙ > 0
3. H₂SO₄(l) + H₂O(l) → H₃O⁺(aq) + HSO₄⁻(aq)
This reaction occurs in the aqueous phase, producing ions in solution. The creation of charged, mobile particles increases disorder, as ions are more disordered than pure liquids. Hence, the entropy increases.
✔ ΔSᵣₓₙ > 0
In summary, changes in the number of gas molecules and the production of ions help predict whether entropy increases or decreases. More gas particles or dissolved ions typically signal an increase in entropy.
