CH67C3~1 - CHAPTER 17 THERMODYNAMICS Problems to prepare...

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CHAPTER 17 THERMODYNAMICS Problems to prepare students for Chem 162 hourly exam III. “THERMODYNAMICS” covers Zumdahl chapter 16. ENTROPY CONCEPTS ENTROPY CALCULATIONS FREE ENERGY CONCEPTS FREE ENERGY CALCULATIONS FREE ENERGY AND EQUILIBRIA CONCEPTS FREE ENERGY AND EQUILIBRIA CALCULATIONS E. Tavss 3/27/11 Chapter 16 practice problems 1
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ENTROPY CONCEPTS 34 Chem 162-2007 Final exam + answers Chapter 17 – Thermodynamics Entropy concepts A 100-mL sample of water is placed in a coffee cup calorimeter. When 1.0 g of an ionic solid is added, the temperature of the resulting solution decreases from 21.5 °C to 20.8 °C as the solid dissolves. For the dissolving of the solid Α. H < 0 Β . S univ > 0 C . S sys < 0 D . S surr > 0 E. ΔS univ < 0 A. False. When there is no subscript, system is assumed. Hence, H = H sys . Since the temperature of the solution (i.e., the surroundings) decreased, that means that the reaction (i.e., the system) is endothermic, i.e., that it required heat energy to dissociate the ions, and this heat energy came from the surrounding solvent. Therefore, H sys = + (or > 0). B. True. Since this is a spontaneous reaction, that is, it went by itself (without any human assistance), then according to the second law of thermodynamics S univ = + (i.e., S univ > 0). C. False. Since the ionic solid dissociated into its individual ions, this means that the ionic solid gained positional freedom. Therefore, S sys = + (or S sys >0). D. False. Since H sys = + (or > 0), then since energy can neither be created nor destroyed (1 st law of thermodynamics) then H surr = - (or < 0). Since S surr = H surr /T, then S surr = -/+ = - = <0. E. False. Since this is a spontaneous reaction, that is, it went by itself (without any human assistance), then according to the second law of thermodynamics S univ = + (i.e., S univ > 0). Chem 162-2007 Exam III + Answers Chapter 17 – Thermodynamics Entropy concepts Chapter 16 practice problems 2
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20 For a spontaneous reaction, the second law of thermodynamics requires: A . ΔS univ >0 B. ΔS sys >0. C. H sys >0 D. H sys <0 E. ΔH surr >0 The second law of thermodynamics says that the entropy of the universe always increases in any spontaneous reaction. A. True B. False. The S sys can be <0, while S univ >0. C. False. Not related to the second law of thermodynamics. Furthermore, a spontaneous reaction may have an increase, a decrease, or no change in enthalpy. D. False. Not related to the second law of thermodynamics. Furthermore, a spontaneous reaction may have an increase, a decrease, or no change in enthalpy. E.
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CH67C3~1 - CHAPTER 17 THERMODYNAMICS Problems to prepare...

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