Spring 2006 CH302 Practice Quiz 1 1 Which of the statements below concerning thermodynamic sign convention is true: 1. w is positive when work is done by the system. 2. ΔΗ is negative when heat is added to the system. 3. work is done on the system when ΔV is positive. 4. ΔSuniv is zero when a reaction is nonspontaneous. 5. ΔH is positive in an exothermic reaction. 2. A friend states that living organisms violate the second law of thermodynamics and consequently we exist only as a figment of our imagination. Your best reply would be: 1. as long as the entropy of the surroundings increased while you were being formed, no laws were broken 2. the second lay of thermodynamics applies to chemistry, not biology 3. a first offense of the second law is only a misdemeanor, don’t sweat the small stuff 4. philosophical arguments are exothermic because they generate a lot of hot air 3 Which of the compounds I) ammonia, ΔGfo = -17 kJ/mol II) calcium carbonate, ΔGfo = -1128 kJ/mol III) water, ΔGfo = -237 kJ/mol IV) benzene, ΔGfo = 124 kJ/mol is/are stable with respect to decomposition into their elements under standard conditions 1. III and IV only 2. I, III and IV only 3. II only 4. I and II only 5. II and III only 6. I, II and III only 7. II, III, and IV only 8. III only 9. Another combination 10. Cannot be determined 4 Calculate the change in entropy of a large pail of water after 1000 J of energy is reversibly removed from the water at 50oC. 1. +3.09 J/K 2. -3.09 J/K. 3. -50J/K 4. +50J/K5 Calculate the normal boiling point of water given that the standard entropy and enthalpy of vaporization of water is +109 J/K/mol and 40.65 kJ/mol, respectively. 1. 0K 2. 100 K 3. 373 K 4. 405 K 5. 450 K 6 For the reaction 2H2O(g) Æ 2H2(g) + O2(g) ΔHro = 484 kJ/mol and ΔSfo = +90J/molK. Which statement is true for this reaction? 1. The reaction is driven by the enthalpy. 2. The reaction will be spontaneous at low temperatures. 3. ΔGfo will be negative at high temperatures. 4. The reaction will not be spontaneous at any temperature. 5 ΔGfo will be positive at high temperatures. 7 Consider the following reaction: 2H2O(g) Æ 2H2(g) + O2(g) Calculate ΔGro for the reactions at 300 K given the formation data above. 1. 457 kJ/mol 2. -457 kJ/mol 3. 510 kJ/mol 4. -214 kJ/mol 8 The entropy of boiling of water is +109.1 J/molK and the enthalpy of boiling of water is +40.6 kJ/mol at 100oC? What is ΔStotal for the melting of ice at 100oC? 1. ΔStotal = -109 J/molK 2. ΔStotal = 0 J/molK 3. ΔStotal = +109 J/molK 3. Cannot determine without ΔSsurr ΔHfo (kJ/mol) Sfo (J/molK) H2O -241.8 188.8 H2 0 130.7 O2 0
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