Chem 2B-quiz 5-021407

Chem 2B-quiz - concentrations(c This reaction is spontaneous at all temperatures(d This reaction is non-spontaneous at all temperatures(e This

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Chem 2B, Winter 2007 Professor Thuc-Quyen Nguyen Name: Quiz #5 02/14/07 1) ( 4 points ) Why change in free energy is used to predict spontaneous processes instead of change in entropy? We can just focus on the system only. If we use the entropy, we need to know the change in entropy of the system and the surroundings to calculate the change in entropy of the universe. From the sign of the ΔS universe, we can predict the process is spontaneous or not. 2) ( 4 points ) Consider the reaction: 2 PbO 2 (s) 2 PbO (s) + O 2 (g) H o = + 117 kJ Which of the following statements concerning this reaction is true? (a) This reaction is non-spontaneous at lower temperatures and spontaneous at higher temperatures. (b) This reaction can never be at equilibrium where all species are present at standard
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Unformatted text preview: concentrations. (c) This reaction is spontaneous at all temperatures. (d) This reaction is non-spontaneous at all temperatures. (e) This reaction is spontaneous at lower temperatures and non-spontaneous at higher temperatures. 3) ( 12 points ) The molar enthalpy of fusion of solid ammonia is 6.65 kJ/mol, and the molar entropy of fusion is 28.9 JK-1mol-1. (a) Calculate the Gibbs free energy change for the melting of 1.00 mol of ammonia at 170 K. (b) Calculate the Gibbs free energy change for the conversion of 3.60 mol of solid ammonia to liquid ammonia at 170 K. (c) Will ammonia melt spontaneously at 170 K? (d) At what temperature are solid and liquid ammonia in equilibrium at a pressure of 1 atm? Chem 2B, Winter 2007 Professor Thuc-Quyen Nguyen...
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This note was uploaded on 08/06/2008 for the course CHEM 2B taught by Professor Nguyen during the Winter '07 term at UCSB.

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Chem 2B-quiz - concentrations(c This reaction is spontaneous at all temperatures(d This reaction is non-spontaneous at all temperatures(e This

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