Question

question 24 (4 points)
δs is positive for the reaction ________.
o a) 2h₂(g) + o₂(g) → 2h₂o(g)
o b) 2no₂(g) → n₂o₄(g)
o c) co₂(g) → co₂(s)
o d) baf₂(s) → ba²⁺(aq) + 2f⁻(aq)

Explanation:

To determine when \( \Delta S \) (entropy change) is positive, we look for an increase in disorder (more moles of gas, or a solid/liquid breaking into ions, etc.).

• Option a: Reactants have \( 2 + 1 = 3 \) moles of gas; products have \( 2 \) moles. Disorder decreases (\( \Delta S < 0 \)).
• Option b: Reactants have \( 2 \) moles of gas; products have \( 1 \) mole. Disorder decreases (\( \Delta S < 0 \)).
• Option c: Gas (more disorder) turns to solid (less disorder). \( \Delta S < 0 \).
• Option d: Solid \( \text{BaF}_2 \) dissociates into \( \text{Ba}^{2+} \) and \( 2\text{F}^- \) ions in solution. A solid breaking into ions increases disorder (\( \Delta S > 0 \)).

Answer:

d) \( \text{BaF}_2 \, (s)
ightarrow \text{Ba}^{2+} \, (aq) + 2\text{F}^- \, (aq) \)