chem6b practice final

chem6b practice final - Chem 6B Practice Final (for the new...

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Chem 6B Practice Final (for the new book and outline) Below you will find a practice final for Chem 6B. The questions are similar to those you might expect to see on the real exam. The test below may be a little longer than the real thing, but there is no guarantee that it is longer or shorter; nor do I promise that all subject areas I will test you on are represented below . Take this practice exam as if it was a real exam, including time and contioions. Good Luck
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1. ª Water gas, a commercial fuel, is made by the reaction of hot coke with steam. C(s) + H 2 O(g) ----> CO(g) + H 2 (g) When equilibrium is established at 800°C the concentrations of CO, H 2 , and H 2 O are 4.00 x 10 -2 , 4.00 x 10 -2 , and 1.00 x 10 -2 mole/liter, respectively. What is the value of Δ G° for this reaction at 800°C? a) 109 kJ b) –43.5 kJ c) 193 kJ d) 16.3 kJ e) none of these 2. ª A mixture of hydrogen and chlorine remains unreacted until it is exposed to ultraviolet light from a burning magnesium strip. Then the following reaction occurs very rapidly: H 2 + Cl 2 -----> 2HCl Δ G = -45.54 kJ Δ H = -44.12 kJ Δ S = -4.76 J/K Select the statement below which BEST explains this behavior. a) The reactants are thermodynamically more stable than the products. b) The reaction has a small equilibrium constant. c) The ultraviolet light raises the temperature of the system and makes the reaction more favorable. d) The negative value for Δ S slows down the reaction. e) The reaction is spontaneous by thermodynamics, but the reactants are kinetically stable. 3. A spontaneous chemical reaction is FAVORED by which of the following? a) increasing energy and increasing entropy b) lowering energy and increasing entropy c) increasing energy and decreasing entropy d) lowering energy and decreasing entropy 4. Which of the following processes result(s) in an increase in the entropy of the system? All systems are closed systems. I. II. Br 2 (g) à Br 2 (l) III. NaBr(s) à Na + (aq) + Br - (aq) IV. O 2 (298 K) à O 2 (373 K) V. NH 3 (1 atm, 298 K) à NH 3 (3 atm, 298 K) a) I b) II, V c) I, III, IV d) I, II, III, IV e) I, II, III, V
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5. For the dissociation reaction of the acid HF HF <–> H + + F - DS is observed to be negative. The BEST explanation for this is: a) This is the expected result since each HF molecule produces two ions when it dissociates. b) Hydration of the ions produces the negative value of Δ S. c) The reaction is expected to be exothermic and thus Δ S should be negative. d) The reaction is expected to be endothermic and thus Δ S should be negative. e) None of these can explain the negative value of Δ S. 6. ª For the reaction A + B <->C + D, Δ H° = +40 kJ and Δ S° = +50 J/K. Therefore, the reaction at standard conditions is a) spontaneous at temperatures less than 10 K. b) spontaneous at temperatures greater than 800 K.
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chem6b practice final - Chem 6B Practice Final (for the new...

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