probset7withanswers

probset7withanswers - Chem33-1 C-hour Problem Set 7 Student...

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Chem33-1, C-hour Problem Set 7 Due Date: Dec. 8, 2007 Student name: ___________________ Student SISD #: __________________ 1. The overall reaction and the value for the equilibrium constant for a hydrogen-oxygen fuel cell at 298K are 2 H 2 (g) + O 2 (g) 2H 2 O(l) K=1.28x10 83 a) Calculate the standard cell potential E 0 as well as Δ G 0 at 298 K for this fuel cell reaction. b) Predict the signs of Δ H 0 and Δ S 0 for the reaction. c) As temperature increases, does the maximum amount of work from the fuel cell increase, decrease, or stay the same? Explain. ANSWER: In the chemical reaction Oxygen is reduced from an oxidation number 0 to -2. Since 2 mols of Oxygen (atoms) appear in the chemical equation, the total number of electrons exchanged in the reaction is n = 4. a) () ( ) V x K n E 23 . 1 10 28 . 1 log 4 0591 . 0 log 0591 . 0 83 0 = = = () ( ) kJ x C J e mol C e mol nFE G 475 10 75 . 4 23 . 1 485 . 96 4 5 0 0 = = = = Δ b) Since the mols of gas decrease as the reaction proceeds, Δ S 0 will be negative. Since Δ G 0 is also negative, Δ H 0 must be negative as well. c) Δ G 0 = w max = Δ H 0 - T Δ S 0 with a negative Δ S 0 implies that with increasing temperature Δ G 0 becomes more positive (= close to zero). Therefore, w max decreases with increasing temperature.
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2. How does the energy of a H 1s orbital compare with that of a Li 1s orbital? a) Why? b) What is meant by the term energy of the orbital? c)
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This note was uploaded on 04/29/2008 for the course CHEM 33 taught by Professor Rose-petruck during the Fall '07 term at Brown.

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probset7withanswers - Chem33-1 C-hour Problem Set 7 Student...

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