Question

Short Answer: (4 points each) 1.) Predict whether the entropy change is positive or negative for each of the following reactions. GIVE YOUR REASON FOR YOUR PREDICTIONS a) 2KC1O4(s) → 2KCIO3() + O2(8) b) H2O → H2O) c) 2Na(3) + H2O → 2NaOH(aq) + H2() d) N2(g) → 2N) 2.) State whether the sign of the entropy change expected for each of the following processes will be positive or negative, and EXPLAIN YOUR PREDICTIONS. a) PC130) + Cl2(e) → PCls(s) b) 2Hgm + O2(g) → 2HgO(s) c) H2(g) → 2H) d) UF6(s) → Us) + 3F2(e)

Answer 1

The factors that lead to an increase in entropy are: (1) a transition from a condensed phase to the vapor phase (2) a reaction that produces more product species than reactant species in the same phase (3) a process where the product molecule has greater molecular complexity relative to the reactant's molecular complexity

(a) PCl3(l) + Cl2(g) → PCl5(s) In this reaction, a gas reacts with a liquid to form a solid. There is a decrease in the number of moles of gas; thus, a decrease in microstates. ΔS is negative.

(b) 2HgO(s) → 2Hg(l) + O2(g) In this reaction, a solid decomposes to produce a liquid and a gas. There is an increase in microstates. ΔS is positive.

(c) H2(g) → 2H(g) In this reaction, there are two moles of gas in the products and one mole of gas in the reactants. An increase in the number of moles of gas means an increase in microstates. ΔS is positive.

(d) U(s) + 3F2(g) → UF6(s) A gas reacts with a solid to form a solid. There is a decrease in the number of moles of gas in the products relative to the reactants; thus, a decrease in microstates. ΔS is negative.