week4key - Chemistry 114 Week 4 Worksheet Spring 2008 You...

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Chemistry 114 Week 4 Worksheet Spring 2008 You may need to use tables from your text to solve the following problems. 1. Calculate Δ G ˚ for each reaction at 298.15 K in two ways: first, use Δ G ˚ f values, and second, use Δ H ˚ f and S ˚ values. Make sure to balance the reactions first! a. Mg(s) + O 2 (g) MgO(s) b. CH 3 OH(g) + O 2 (g) CO 2 (g) + H 2 O(g) 2. Use S ˚ values to calculate the entropy change, Δ S ˚, for each of the following processes at 298.15 K and comment on the sign of the change. a. KOH(s) KOH(aq) b. Na(g) Na(s) c. Br 2 (l) Br 2 (g) d. HCl(g) HCl(aq) (a) Δ S º = S º[KOH(aq)] – S º[KOH(s)] Δ S º = 1 mol (91.6 J/K·mol) – 1 mol (78.9 J/K·mol) = 12.7 J/K A positive S º indicates an increase in entropy (b) Δ S º = S º[Na(s)] – S º[Na(g)] Δ S º = 1 mol (51.21 J/K·mol) – 1 mol (153.765 J/K·mol) = –102.56 J/K A negative Δ S º indicates a decrease in entropy (c) Δ S º = S º[Br 2 (g)] – S º[Br 2 ( l )] Δ S º = 1 mol (245.42 J/K·mol) – 1 mol (152.2 J/K·mol) = 93.2 J/K A positive S º indicates an increase in entropy (d) Δ S º = S º[HCl(aq)] – S º[HCl(g)] Δ S º = 1 mol (56.5 J/K·mol) – 1 mol (186.2 J/K·mol) = –129.7 J/K A negative S º indicates a decrease in entropy 3. Calculate the standard molar entropy change for each of the following reactions at 25˚ C. Comment on the sign of Δ S ˚. a. 2 Na(s) + 2 H 2 O(l) 2 NaOH(aq) + H 2 (g) b. Na 2 CO 3 (s) + 2 HCl(aq) 2 NaCl(aq) + H 2 O(l) + CO 2 (g) (a) Δ S º = 2 S º[NaOH(aq) ] + S º[H 2 (g)] – {2
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This note was uploaded on 04/07/2008 for the course CHEM 114 taught by Professor Jursich during the Spring '08 term at Ill. Chicago.

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week4key - Chemistry 114 Week 4 Worksheet Spring 2008 You...

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