Kwantlen Polytechnic University Chemistry 1105 S10 Spring Term Test No. 3 Thursday, April 4, 2013

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1 Kwantlen Polytechnic University Chemistry 1105 S10 Spring Term Test No. 3 Thursday, April 4, 2013 Name: Student Number Instructions: Ensure that this exam contains all eight pages including this page. A periodic table sheet is also provided. Read the exam carefully and judge your time accordingly. If you need extra space, use the back of a preceding page and clearly indicate the question number. Rough work may also be done on the back of a preceding page. All work must be shown on word problems and conversions to receive credit. A calculator is allowed. Express all numerical answers with the correct number of significant figures. Time allowed: 1 hr 50 minutes Maximum Score: 44 IMPORTANT INFORMAION: PV = nrt T(K) = T( C) atm = 760 torr = 760 mmhg R = L atm/mol K q = m C s T (C s = specific heat capacity) q = C cal T (C cal = heat capcitiy) For all ph calculations, assume T = 25 C K w = [H + ][OH - ] = 1.0 x ph = -log[h + ] [H + ] = [H 3 O + ] = 10 -ph

2 2 Part I: Multiple choice and short answer Multiple choice: Circle the correct answer (1 mark each). 1. Which of the following would have the lowest gas density? a) Ne b) O 2 c) H 2 d) He e) N 2 2. Which of the following samples will have the highest pressure if they are all at the same temperature and in identical containers (same volumes)? a) 20.0 g CO 2 (g) b) 20.0 g NH 3 (g) c) 20.0 g He (g) d) 20.0 g Cl 2 (g) e) All of these samples will have the same pressure. 3. Which of the following will cause the volume of an ideal gas to increase by a factor of 3? a) Raising the temperature from 25 C to 75 C at constant pressure. b) Lowering the absolute temperature by a factor of 3 at constant pressure. c) Raising the absolute temperature by a factor of 3 at constant pressure. d) Lowering the absolute temperature by a factor of 3 while raising the pressure by a factor of 3 e) Raising the pressure by a factor of 3 while the temperature stays constant. 4. Complete the sentence: An exothermic reaction a) has a positive ΔH and absorbs heat from the surroundings. b) has a positive ΔH and gives off heat to the surroundings. c) has a negative ΔH and gives off heat to the surroundings. d) has a negative ΔH and absorbs heat from the surroundings. 5. Given that at room temperature: 2 NO(g) + Br 2 (g) 2NOBr (g) K c = 3.00 Calculate K c (at the same temperature) for NOBr (g) NO(g) + ½ Br 2 (g) a) b) c) d) 1.73 e) Two aqueous solutions are both at room temperature and are then mixed in a coffee cup calorimeter. The reaction causes the temperature of the resulting solution to fall below room temperature. Which of the following statements is TRUE? a) The reaction is exothermic. b) The reaction is endothermic. c) No heat is released or absorbed in the reaction. d) There is not enough information to tell if heat released or absorbed in the reaction.

3 3 7. How much heat is evolved with the production of 323 g of Ca(OH) 2 according to the following equation: CaO (s) + H 2 O (l) Ca(OH) 2 (s) H = kj a) 284 kj b) 2.11 x 10 4 kj c) 376 kj d) 156 kj e) 272 J 8. The standard enthalpy of formation H o f of NH 4 NO 3 (s) is kj/mol. Which of the following thermochemical equations is correct? a) 2N(g) + 4H(g) + 3O(g) NH 4 NO 3 (s) H = kj b) N 2 (g) + 2H 2 (g) + 3/2 O 2 (g) NH 4 NO 3 (s) H = kj c) NH 3 (l) + HNO 3 (aq) NH 4 NO 3 (s) H = kj d) NH 4 + (aq) + NO 3 - (aq) NH 4 NO 3 (s) H = kj e) NH 4 + (s) + NO 3 - (s) NH 4 NO 3 (s) H = kj 9. Which of the following will have the LOWEST ph? a) 0.10 M HCl b) 10.0 M HNO 3 c) 0.10 M HC 2 H 3 O 2 d) 10.0 M HCN e) 0.05 M HF 10. Which of the following solutions will be BASIC? a) 0.10 M NaCl b) 0.10 M NH 4 Cl c) 0.10 M NaClO d) all of the above will be basic a) only b and c e) none will be basic 11. For the following reaction, indicate whether the following statements are true or false: (3 mark) CH 4 (g) + H 2 O (g) C(s) + 3 H 2 (g) + O 2 (g) K c = 458, H is positive If temperature is increased, K c decreases If H 2 gas is removed, moles of O 2 gas will decrease. If the container volume is decreased, K c will decrease.

4 4 Part II: Show your work. All work must be shown for full credit. 1. (5 marks) 4.94 g H 2 O 2 (l) is heated in a 3.50 L closed reaction vessel until it decomposes completely as follows: 2 H 2 O 2 (l) O 2 (g) + 2H 2 O (g) (Assume that the temperature remains constant at 250 C) a) How many moles of each gas forms in the complete reaction? b) What are the mole fractions of O 2 (g) and H 2 O (g) after the reaction? c) Calculate the total pressure and the partial pressures of O 2 (g) and H 2 O (g) after the reaction.

5 5 2. (2 marks) Use the ΔH f information provided to calculate ΔH rxn for the following: SO 2 Cl 2 (g) + 2 H 2 O(l) 2 HCl(g) + H 2 SO 4 (l) ΔH rxn =? ΔH f (kj/mol) SO 2 Cl 2 (g) -364 H 2 O(l) -286 HCl(g) -92 H 2 SO 4 (l) (4 marks) Given the following thermochemical equations: C 3 H 8 (g) + 5O 2 (g) 3CO 2 (g) + 4H 2 O (l) ΔH = kj C(graphite) + O 2 (g) CO 2 (g) ΔH = kj 2H 2 O (l) 2H 2 (g) + O 2 (g) ΔH = kj Calculate ΔH for the equation: 3C(graphite) + 4H 2 (g) C 3 H 8 (g)

6 6 4. (8 marks) Consider the reaction 2 HCl(aq) + Ca(OH) 2 (aq) CaCl 2 (aq) + 2 H 2 O(l) H = -118 kj a) ml of 1.50 M HCl is mixed with ml M Ca(OH) 2 in a coffee-cup calorimeter. Both solutions start at 22.4 C. Assuming all heat from the reaction is transferred to the solution, and that the heat capacity of the solution is that of water (4.184 J/g C), calculate the final temperature of the solution after the reaction is complete. (4 marks) b) What is the ph of the M Ca(OH) 2 solution from part (a) before mixing? (2 marks) [NOTE: this problem can be done without completing part (a)] c) If the final solution above in part (a) (after the reaction) is brought to 25 C, calculate the ph. (2 marks)

7 7 5. (4 marks) Consider the following reaction and its equilibrium constant: I 2 (g) + Br 2 (g) 2 IBr(g) K c = A reaction mixture contains M I 2, M Br 2. Calculate the concentrations of all gases at equilibrium. 6. (3 marks) Consider the following reaction and its equilibrium constant at 150 C: 4 CuO(s) + CH 4 (g) CO 2 (g) + 4 Cu(s) + 2 H 2 O(g) K c = 1.10 A 1.0-L reaction mixture contains M CH 4, M CO 2 and M H 2 O. In which direction will the reaction shift to reach equilibrium?

8 8 7. (3 marks) Calculate the ph of a 0.30 M solution of sodium acetate acid, NaC 2 H 3 O 2. The K a of acetic acid is 1.8 x (2 marks) The ph of a M solution of hypobromous acid, HBrO, is Calculate K a.