CHEM 1032 PRACTICE EXAM IV CLASS SPRING 2017

Transcription

1 1 CHEM 1032 PRACTICE EXAM IV CLASS SPRING 2017 (You may need a periodic table. Useful information is on the last page). 1. Which of the following is a non-spontaneous reaction under standard conditions? A. NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) B. 2 K(s) + 2 H 2 O(l) 2 KOH(aq) + H 2 (g) C. Pb(NO 3 ) 2 (aq) + 2 NaCl(aq) 2 NaNO 3 (aq) + PbCl 2 (s) D. C 6 H 12 O 6 (s) 2 CO 2 (g) + 2 C 2 H 5 OH(l) 2. Which of the following has the highest standard molar entropy, S o? A. H 2 (g) B. Ne(g) C. F 2 (g) D. HF(g) 3. Which of the following reactions would be predicted to have negative value for S o rxn? A. C(s) + O 2 (g) CO 2 (g) B. 2 CO 2 (g) 2 CO(g) + O 2 (g) C. 2 H 2 (g) + O 2 (g) 2 H 2 O(l) D. 2 O 3 (g) 3 O 2 (g) 4. Which of the following statements is correct? A. The total enthalpy of the earth is constant B. The entropy of a perfect crystal at absolute zero is zero C. The total enthalpy of the universe is increasing D. For any non-spontaneous process, the entropy of the universe increases 5. If a reaction has H positive and S positive, then: A. the reaction is spontaneous at all temperatures B. the reaction is spontaneous at low temperatures C. the reaction is non-spontaneous at all temperatures D. the reaction is spontaneous at high temperatures 6. When a reaction is at equilibrium under non-standard conditions, then: A. G o rxn = 0 B. K = 1 C. G rxn = 0 D. G o rxn = G rxn

2 2 The following 3 reactions appeared on a white board in Sheldon and Leonard s apartment in an episode of the TV show The Big Bang Theory. Use these equations and the data table below to answer questions Reaction 1: Reaction 2: Reaction 3: 2 H 2 (g) + N 2 (g) N 2 H 4 (g) N 2 H 4 (g) + H 2 (g) 2 NH 3 (g) 3 H 2 (g) + N 2 (g) 2 NH 3 (g) H 2 (g) N 2 (g) NH 3 (g) N 2 H 4 (g) ΔH o f kj/mol S o J/(mol K) ΔG o f kj/mol Which reaction has a positive change in entropy? A. Reaction 1 B. Reaction 2 C. Reaction 3 D. All 3 Reactions 8. What is the change in entropy of the surroundings, S o surr, for Reaction 1 at 25 o C? A J/K B J/K C J/K D. 322 J/K 9. Is Reaction 1 spontaneous at 25 o C? A. No B. Yes C. Insufficient information 10. At what temperature will Reaction 3 become non-spontaneous? A. At temperatures below 462 o C B. At temperatures below 0.46 K C. At temperatures above 189 o C D. At temperatures above 735 K 11. Reaction 3 is an equilibrium reaction: 3 H 2 (g) + N 2 (g) 2 NH 3 (g). Which of the following is a true statement concerning the spontaneity of this reaction under standard conditions? A. The forward reaction is non-spontaneous and the reverse reaction is spontaneous. B. The forward reaction is spontaneous and the reverse reaction is non-spontaneous. C. The forward and the reverse reactions are both spontaneous. D. The forward and the reverse reactions are both non-spontaneous. 12. In the industrial synthesis of ammonia (the Haber process), Reaction 3 is carried out at a temperature of 500 o C, and at the following partial pressures: P H2 = 2.5 atm, P N2 = 7.5 atm, P NH3 = 0.17 atm. What is the free energy change of the forward reaction under these non-standard conditions? A. 32 kj B. 47 kj C. 62 kj D. 85 kj

3 3 There are two forms of tin: White powdery Sn, G o f = 0 kj/mol; Grey metal Sn, G o f = kj/mol. Use this information to answer questions The two forms of tin are called: A. isomers B. isotopes C. megatropes D. allotropes 14. Which form is the most thermodynamically stable form of tin? A. White powdery Sn B. Grey metal Sn C. Insufficient information 15. Will the reaction: Grey metal Sn White powdery Sn, occur at 25 o C? A. Yes B. No C. Insufficient information 16. Tin cans do not spontaneously turn into white powdery tin, because: A. the reaction is spontaneous at only high temperatures B. the activation energy is very high and the rate of the reaction is very slow C. the reaction is non-spontaneous at room temperature D. the activation energy is very low and the rate of the reaction is very slow The following redox reaction occurs in acidic solution: S 2 O 3 2 (aq) + Cl2 (g) SO 4 2 ( aq) + Cl (aq) The oxidation number of all O atoms is 2. Answer questions on this reaction. 17. The oxidation numbers of the S atoms in S 2 O 3 2 and in SO 4 2 are, respectively: A. +4 and +2 B. +2 and +4 C. +3 and +6 D. +2 and How many electrons are involved in the oxidation half reaction? A. a loss of 8 e B. a gain of 4 e C. a gain of 8 e D. a loss of 4 e 19. To balance the redox reaction, where should you place the H + (aq) and H 2 O(l)? A. H + (aq) on the left and H 2 O(l) on the right B. H + (aq) on the right and H 2 O(l) on the left C. H + (aq) and H 2 O(l) both on the right D. H + (aq) and H 2 O(l) both on the left 20. When the redox equation is balanced, what will be the coefficients a, b, c and d in: a S 2 O 3 2 (aq) + b Cl2 (g) c SO 4 2 ( aq) + d Cl (aq) A. a = 1, b = 1, c = 2, d = 2 B. a = 2, b = 1, c = 4, d = 2 C. a = 1, b = 4, c = 2, d = 8 D. a = 4, b = 1, c = 8, d = 2

4 4 The electrochemical cell shown below is assembled and a spontaneous reaction occurs. Use the table of standard reduction potentials, and the diagram below, to answer questions Solution Y contains: A. Au + (aq) ions B. Au 3+ (aq) ions C. Ni 2+ (aq) ions D. Ni 3+ (aq) ions 22. Electrons flow from: A. Ni to Au B. Au to Ni C. Solution X to Solution Y D. Solution Y to Solution X 23. Cations in the salt bridge flow from: A. Ni to Au B. Au to Ni C. Solution X to Solution Y D. Solution Y to Solution X 24. What is being reduced? A. Au(s) B. Au 3+ (aq) C. Ni(s) D. Ni 2+ (aq) 25. The value of E o cell is: A V B V C V D V 26. If the mass of the electrodes is monitored during the reaction we would find that: A. Ni increases, Au decreases B. Ni decreases, Au decreases C. Ni decreases, Au increases D. Ni increases, Au increases 27. How many electrons are transferred from the reducing agent to the oxidizing agent? A. 2 B. 3 C. 6 D The value of G o for the reaction at 25 o C is: A kj B kj C kj D. 967 kj

5 5 29. The value of K for the reaction at 25 o C is approximately: A B C D If Solution X has a concentration of 2.00 M and Solution Y has a concentration of M, the cell potential at 25 o C under these non-standard conditions would be: A V B V C V D V

6 6 Useful Information: 0 ºC = 273 K R = J/(mol. K) S univ = S sys + S surr S surr = H rxn /T G = H T S G rxn = G o rxn + RTlnQ G = RTlnK E cell = E cathode E anode G = nfe cell F = 96,485 C/mol e E cell = logk (at T = 25 C) n E cell = E o cell logq n (at T = 25 C)