The Last Pages of This Examination Are Reference Tables

Chemistry 116: General Chemistry Syracuse University Project Advance Exam #3, Spring 2003

Name Date

The last pages of this examination are reference tables [Gas constant = 0.00831 kJ/mol K; 1 faraday = 96.5 kJ/V mol e-; R = 8.31 x 10-3 kJ/molK]

(1) The heat of vaporization of diethyl ether at its boiling point (35.6° C) is 26.7 kJ/mol. What is the change in entropy of the system when 1.34 mol of diethyl ether vaporizes at its boiling point?

(a) -86.5 J/K (b) +86.5 J/K (c) -116 J/K (d) +116 J/K (e) None of the above

(2) Predict the sign of S°, if possible, for the following reaction:

2C(s) + O2(g) ------> 2 CO(g)

(a) S° is positive (b) S° is negative (c) S° is zero (d) cannot predict the sign of S°

(3) Calculate S° for the following reaction at 25° C using standard entropy value from the table:

2 Na(s) + Cl2(g) ------> 2 NaCl(s)

Na(s) S° = 51.4 J/(mol K) Na(aq) S° = 60.2 J/(mol K) Cl2(g) S° = 223.0 J/(mol K) Cl-(aq)(s) S° = 55.1 J/(mol K) NaCl(s) S° = 72.1 J/(mol K)

(a) -181.6 J (b) +181.6 J (c) -202.3 J (d) +202.3 J (e) -78.9 J (4) For a reaction with H° > 0 and S° > 0, you can deduce that the reaction will be:

CHE 116 1 Spring 2003 Exam Questions (a) spontaneous at all temperatures. (b) nonspontaneous at all temperatures. (c) spontaneous at low temperature; nonspontaneous at high temperature. (d) nonspontaneous at low temperature; spontaneous at high temperature. (e) none of the above.

(5) For a mixture if He(g) in Ar(g), the standard entropy of mixing (S°) is:

(a) positive (b) negative (c) sometimes positive and sometimes negative (d) cannot tell from the information provided.

(6) In a spontaneous process, a certain system, held at the constant temperature 300 K, absorbs 30 J of heat energy. From your knowledge of the various statements of the second Law of Thermodynamics, which of the following is the most accurate statement you can

make about Ssystem for this spontaneous process?

(a) Ssystem < -0.1 J/K

(b) Ssystem > 0.1 J/K

(c) Ssystem < -10 J/K

(d) Ssystem0 J/K (e) none of these

(7) Calculate G° for the following reaction at 500K.

Cu(s) + H2O(g) ------> CuO(s) + H2(g)

H°f (kJ/mol) S° (J/K) Cu(s) 0 33.3 H2O(g) -241.8 188.7 CuO(s) -155.2 43.5 H2(g) 0 130.6

(a) +110.6 kJ (b) -86.6 kJ (c) +23.9 kJ (d) -62.6 kJ (e) +301 kJ

(8) For a certain hypothetical reaction at 27oC, Ho = 100 kJ/mole, and So = 500 J/mole. Calculate the GO for this reaction.

CHE 116 2 Spring 2003 Exam Questions (a) –13400 kJ/mole (b) 86.5 kJ/mole (c) –149900 kJ/mole (d) 250 kJ/mole (e) –50 kJ/mole

(9) For the reaction: 3 C(s) + 4 H2(g) <======> C3H8(g)

S° = -29 J/(mol K) H° = -103.8 kJ/mol

Calculate the equilibrium constant at 25° C for the reaction above.

(a) 1.04 (b) 0.962 (c) 2.09 x 10-17 (d) 4.79 x 1016 (e) 2.1 x 1032

(10) What is the minimum temperature required for the spontaneous conversion of CCl4(g) when H° is 573 kJ/mol and S° is 1640 J/(mol K)

(a) 76° C (b) 89° C (c) 189° C (d) 215° C (e) 349° C

(11) Which process below leads to a decrease in the entropy of the system as the process proceeds?

I. 2H2O (s)  2H2O (l) II. CaO (s) + CO2 (g)  CaCO3 (s) III. 2C (s) + O2 (g)  2CO (g) IV. 2MnO2 (s)  2MnO (s) + O2 (g) V. O (g) + O2 (g)  O3 (g)

(a) Only II leads to a decrease in entropy of the system (b) Only I leads to a decrease in entropy of the system (c) Both I and III leads to a decrease in the entropy of the system (d) Both II and V lead to a decrease in the entropy of the system (e) None of the processes lead to a decrease in the entropy of the respective systems.

o o (12) For the reaction: H2 (g) + S (s)  H2S (g), H = -20.2 kJ/mole and S = +43.1 J/mole-K. Which of the following statements is true?

(a) The reaction is only spontaneous at low temperatures. (b) The reaction is spontaneous at all temperatures. (c) Go becomes less favorable as T is raised. CHE 116 3 Spring 2003 Exam Questions (d) The reaction is spontaneous only at high temperatures. (e) At 25oC and under standard conditions, the reaction is at equilibrium.

(13) Calculate the voltage of a cell in which the following reaction occurs:

+ 2+ Zn(s) + 2H (aq, 0.001 M) ------> Zn (aq, 1 M) + H2(g, 1 atm)

The standard reduction potential for zinc is:

Zn2+ + 2 e- <======> Zn E° = -0.763

(a) +0.73 V (b) +0.41 V (c) +0.58 V (d) +0.70 V (e) –0.41 V

(14) Which of the following reactions is a redox reaction?

I. K2CrO4 + BaCl2 ------> BaCrO4 + 2KCl 2+ - II. Pb2 + 2Br ------> PbBr III. Cu + S ------> CuS

(a) only I (b) only II (c) only III (d) I and II (e) all three (I, II and III)

(15) What is the coefficient of Fe3+ when the following equation is correctly balanced?

CN- + Fe3+ ------> CNO- + Fe2+ (basic solution)

(a) 1 (b) 2 (c) 3 (d) 4 (e) 5

(16) What is the coefficient of Fe3+ when the following equation is correctly balanced?

- As + ClO3 ------> H3AsO3 + HClO (acidic solution)

(a) 1, 1, 1, 1 (b) 2, 1, 2, 1 (c) 4, 3, 4, 3 (d) 2, 2, 4, 1 CHE 116 4 Spring 2003 Exam Questions (e) None of the above

(17) What process occurs at a cathode?

(a) oxidation (b) reduction (c) oxidation and/or reduction (d) neither oxidation nor reduction (e) None of the above

(18) What is the equilibrium constant for the following reaction at 25oC? Given the reduction potential of Co = -0.227 V and the reduction potential for H+ = 0 V.

+ +2 Co (s) + 2H (aq)  Co (aq) + H2 (g)

(a) 0.277 (b) 4.31 x 10-10 (c) 2.32 x 109 (d) 4.82 x 104 (e) none of these

(19) Nickel is electroplated from a NiSO4 solution. If a constant current of 5.00 amp is applied by an external power supply, how long will it take to deposit 100 g of Ni?

(a) 18.3 hours (b) 2.40 days (c) 63.1 minutes (d) 56.7 seconds (e) 1.20 seconds

+2 + (20) Consider the cell: Zn (s) | Zn (0.10 M) || H (aq) | H2 (g) (1 atm)

This cell can be used to provide a measure of the pH in the cathode compartment. What is the pH in the cathode compartment if the cell emf is measured to be 0.60 V when [Zn+2] = 0.10 M + and PH2 = 1.00 atm? ( Recall pH = - log [H ] )

(a) 1.00 (b) 5.59 (c) 0.79 (d) 3.25 (e) none of these

CHE 116 5 Spring 2003 Exam Questions