Thermodynamics. 1. Which of the following processes causes an entropy decrease?

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1 Thermodynamics 1. Which of the following processes causes an entropy decrease? A. boiling water to form steam B. dissolution of solid KCl in water C. mixing of two gases in one container D. beach erosion E. freezing water to form ice 2. Which one of the following substances has the highest entropy at 25 o C? A. 1 mole of NH 3 (g) B. 1 mole of Ne(g) C. 1 mole of Ar(g) D. 1 mole of H 2 O(l) E. 1 mole of H 2 O(s) 3. Which of the following processes cause an entropy decrease? A. Dissolving solid NaCl in water. B. Boiling water to form steam. C. Cooling water from 80 o C to 20 o C. D. Melting ice to form water. E. None of the above processes decrease entropy. 4. Which one of the following substances has the highest absolute entropy at 25 o C? A. NH 3 (g) B. Ne(g) C. H 2 O(l) D. C(s) E. H 2 (g) 5. Which equation represents a reaction that is decreasing in entropy as the reaction proceeds? A. CaCO 3 (s) CaO(s) + CO 2 (g) B. 2 C(s) + O 2 (g) 2 CO(g) C. 2 Na(s) + 2 H 2 O(l) 2 NaOH(aq) + H 2 (g) D. 2 H 2 (g) + O 2 (g) 2 H 2 O(l) E. N 2 O(g) + NO 2 (g) 3 NO(g)

2 6. Calculate S o (J mol 1 K 1 ) for the following reaction. (See appendix for S o values.) A. 528 B. 327 C. 268 D. 176 E FeO(s) + O 2 (g) 2 Fe 2 O 3 (s) 7. Consider the following reaction occurring in an automobile engine: 2 C 8 H 18 ( ) + 25 O 2 (g) 16 CO 2 (g) + 18 H 2 O(g) The signs of H, S, and G would be: H S G A. + + B. + + C. + + D. + E Consider the following reaction: A+B C+D This reaction is always spontaneous when H is and S is. H S A. + + B. C. + D Consider the reaction (demonstrated in class) which occurs when a balloon filled with H 2 (g) and O 2 (g) is ignited. The signs of H, S and G would be H S G A. B. + C. + D. + E H 2 (g)+o 2 (g) 2H 2 O(g)

3 10. Which of the following statements is false? A. A spontaneous reaction can be endothermic. B. A spontaneous reaction can be very slow. C. A catalyst can be used to speed up some spontaneous reactions. D. For a system at equilibrium G rxn is zero. E. A spontaneous reaction must have a negative enthalpy change. 11. Which one of the following process has a negative standard free energy change at 25 C? A. CO 2 (g)+2h 2 O( ) CH 4 (g)+2o 2 (g) B. 2Na(s)+2H 2 O( ) 2NaOH(aq)+H 2 (g) C. 2H 2 O( ) 2H 2 (g)+o 2 (g) D. 2KCl(s) 2K(s)+Cl 2 (g) E. AgCl(s) Ag + (aq)+cl (aq) 12. A flask containing a mixture of solids given in the equation below was placed on a board in a puddle of water. When the salts were mixed, a reaction occurred and as a result the water froze causing the flask to freeze to the board. Ba(OH) 2. 8H 2 O(s) + 2NH 4 SCN(s) Ba(SCN) 2 (aq) + 2NH 3 (g) + 10H 2 O( ) For this reaction: A. H is negative and S is negative. B. H is positive and S is positive. C. H is negative and S is positive. D. H is positive and S is negative. E. H and S are both zero. 13. Dissolving ammonium chloride (NH 4 Cl) in water lowers the temperature of the system. For this dissolving process: A. H is negative and S is negative B. H is positive and S is positive C. H is negative and S is positive D. H is positive and S is negative E. H is positive and S is zero

4 14. Assuming H and S do not vary with temperature, at what temperature will the reaction below become spontaneous? C(s) + H 2 O(g) CO(g) + H 2 (g) H o = kj mol 1 S o = J mol 1 K 1 A. 272 o C B. 1 o C C. 552 o C D. 710 o C E. 947 o C 15. The entropy of vaporization ( S o vap) for benzene is 96.4 J/K-mol. The enthalpy of vaporization ( H o vap) is 33.9 kj/mol. What is the normal boiling point (in o C) for benzene? A. 2.8 B C. 100 D. 54 E For the reaction: 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) G o = kj H o = kj S o = J/K Assuming H o and S o do not vary with T, what temperature would cause the reaction to become nonspontaneous? A. The reaction would be spontaneous at all temperatures. B o C C. 739 o C D. 764 o C E. The reaction would be nonspontaneous at all temperatures 17. Determine the value of G o (in kj mol 1 ) for the following reaction taking place at 25 o C. (See appendix C for G o f values) 2C 2 H 6 (g) + 7 O 2 (g) 4CO 2 (g) + 6H 2 O(g) A B C D. 590 E. 557

5 18. Consider the following table of thermodynamic data. Substance G o f (kj/mol) S o (J/mol K) NO(g) NO 2 (g) N 2 O(g) What is the value of H o (in kj) at 25 o C for the reaction shown below? A B. 5.5 C D E N 2 O(g) + NO 2 (g) 3NO(g) 19. K a for the following reaction at 298K is CH 3 COOH(aq) H + (aq) + CH 3 COO (aq) What is the value of G when [CH 3 COOH]=0.100 M, [CH 3 COO ]=0.100 M and [H + ]= M? A kj/mole B kj/mole C kj/mole D kj/mole E kj/mole 20. Calculate the magnitude of the equilibrium constant at 25 o C for the following reaction, given: G o f (HBr) = kj/mol, G o f (HCl) = kj/mol and G o f (Br 2 ) = 3.14 kj/mol G o f (Cl 2 ) = 0 kj/mol 2 HBr(g) + Cl 2 (g) 2 HCl(g) + Br 2 (g) A B C D E

6 21. Calculate the value of G o (in kj/mole) for this reaction at 25 o C. N 2 (g) + 3H 2 (g) 2NH 3 (g) K= A. 22 B. 50 C. 4.2 D. 25 E Which one of the following statements is true about the equilibrium constant for a reaction if G o for the reaction is negative? A. K = 0 B. K = 1 C. K > 1 D. K < 1 E. K < 0

1 A reaction that is spontaneous.

Slide 1 / 55 1 A reaction that is spontaneous. A B C D E is very rapid will proceed without outside intervention is also spontaneous in the reverse direction has an equilibrium position that lies far to