Midterm Exam - QUEEN’S UNIVERSITY FACULTY OF APPLIED...

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Unformatted text preview: QUEEN’S UNIVERSITY FACULTY OF APPLIED SCIENCE APSC 132 Chemistry Midterm Examination May 4, 2002 Duration: 3.0 h CASIO 991 AND APPROVED GOLD STICKER CALCULATORS ARE PERMITTED. The examination is divided into three parts. The mark breakdown for each part is shown below. Part A: nine short knowledge questions (1 mark each) 9 marks Part B: nine short calculations problems (2 marks each) 18 marks Part C: four major problems 43 marks Total 70 marks The answers to Parts A and B will be placed on a computer-marked sheet. To answer these questions: You must use a soft-lead pencil (HB or softer). The scanner will not read ink no matter how black a mark it makes. Do not bend or fold the answer sheet in any way or it will become jammed in the scanner. Write and code you name and student number on the answer sheet in the upper left-hand comer. Do not mark the computer answer sheet in any way except to code in the answers. You will have difficulty erasing any mistakes once they’ve been coded. Make sure you’ve coded in all of the answers. No marks are deducted for wrong answers. Answer all questions from Part C in the examination booklets provided. Put your student number and name on all booklets. If the instructor is unavailable in the examination room and if doubt exists as to the interpretation of any question, the candidate is urged to submit with the answer paper a clear statement of any assumptions made. Some useful equations, data and a periodic table may be found at the end of this examination paper. Instructor:Wm.Newstead Part A: Each correct answer is worth 1 mark 1. In which of the following processes is the work done by the system the largest at 25°C? a. An isothermal free expansion of an ideal gas from 1 L to 10 L. b. An isothermal expansion of an ideal gas from 1L to 10 L against an opposing pressure of 1 atm. An isothermal expansion of an ideal gas from IL to 10L against an opposing force of 5 atm An isothermal reversible expansion of an ideal gas from IL to 10 L. 2. For the hypothetical reactions 1 and 2 below, K1 = 103 and K2 = 105. l. A+2B¢>AB2 2. A+B¢>AB 3 AB2¢>AB+B What is the value of K for reaction 3? 10'8 b. 10‘2 c. 102 d. 108 3. Consider the equilibrium system, A(g) + B(g) ¢i> C(g) + D(g). At 25°C, the value of K is 1.2 x 10'3. At 50°C, the val - ofK is 3.4 x 10']. The reaction is: a. exothermic endothermic c. more information needed d. impossible to tell \w 4. Calculate the pOH of .10 M solution of Ba(OH)2. a. 13.30 .70 c. 1.00 d. 13.00 5. The sodium salt NaA of a weak acid is dissolved in water. No other substance is added. Which of these statements is true? a. [W] = [A'] b. [H] = [OH'] 0. [OH'] = [A'] HA] = [OH‘] 6. For the process benzene(l) -) benzene(g) at a constant pressure of 1 atm, AH° = 30.5 kJ/mol and AS" = 86.4 J/mol.K. Assuming these values are independent of temperature, w t is the normal boiling point of benzene? a. 0°C 0°C 0. 353°C d. —80°C 7. Which statement about equilibrium is NOT true? a. When a system is disturbed, it responds to restore equilibrium. b. The value of the equilibrium constant for a reaction does not depend on the direction from which equilibrium is attained. c. A system moves spontaneously toward a state of equilibrium. The equilibrium constant is independent of temperature. 8. £3 9. U.) Consider the numbered processes. l.A-)2B AH; 2.B-)C+D AHZ 3.E-)2D AH3 Find AH for the process A -) 2C + E a. AHl + AHz + AH3 b. AH1 + AH2 C. AH] + AHz - AH3 AH1 + 2AH2 - AH3 For the reaction, 3 H2(g) + N2(g) 41> 2NH3(g) What is the relationship between Kc and KD at temperature T? a. Kc: K, b. Kp = Kc(RT)2 @(c = Kpmr)2 d. K, =x/ K, Part B: Each correct answer is worth 2 marks 10. In an irreversible isothermal process, the pressure on 1.00 mol of an ideal gas changes from 2.50 11. 12. 13. 14. 15. éricky: This solution produces a buffer solution.) atm to 6.50 atm at 27°C. Q is equal to: (Note: 1 L.atm = 101.3 J) a. —2.38 kJ b. 2.38 k} c. 3.99 k] 3.99 k] For a weak acid HX, the pH of a 0.10 M solution is 5.83 at 25°C. What is AG° for the dissociation reaction at 25°C? @61kJ a. —61 k] b. —30 kJ For the reaction H2(g) + 12(g) ¢i> 2 Hl(g), Kp = 45.9 at 763 K. An equilibrium mixture at that temperature contains gaseous hydrogen iodide at a partial pressure of 4.00 atm and hydrogen gas at a partial pressure of 0.200 atm. What is the partial pressure of the iodine gas? a. 0.200 atm b. 0.436 atm @174 atm d. 0.574 atm The pH of a 0.150 M solution of a weak base is 10.98. Calculate the pH of a 0.0400 M solution of 6 base? a.10.5 10.7 How many moles of benzoic acid, a monoprotic acid with Ka = 6.4 x 105, must be dissolved in 500 mL of water to produce a solution with = 2.50? a. 1.6x 10'1 b. 2.0x 10'2 7.8x 10'2 c. 30 kJ c.11.2 d.11.5 .d. 0.50 Calculate the pH of a solution made by mixing 100.0 mL of a 0.300 M NH3 with 100.0 mL of0.100 M HCl. Kb for NH3 is 1.8 x10‘5. 9.56 b. 4.44 c. 10.6 d. 3.40 16. The pH of a 2.1 x 10’3 M weak base solution is 9.87. Calculate Kb for this base. a. 1.2x 10'4 b. 6.4x 10'8 @2.6x10‘6 d. 8.7x 10‘18 17. For the reaction 2 SOz(g) + 02(g) <$ 2 SO3(g), AHO = -200 k] and AS° = —187 J/K at 25°C. Assuming that AH° and AS° are independent of temperature, calculate the temperature at which KID = 1. a. 970 K 1070 K c. 200 K d. 2070 K 18. In a reversible isothermal process, the pressure on 1.00 mol of an ideal gas changes from 2.50 atm to 6.50 atm at 27°C. alculate AS? a. 7.94 J/K —7.94 J/K C. 13.3 J/K d. —l3.3 J/K Part C: This section of the examination is worth 43 marks. The questions in this section should be answered in the examination answer booklets. Problem #1 ( 8 marks: Suppose 93.0 g of Hl(g) is placed in a 10.24 L glass vessel and heated to 1107 K. At this temperature, equilibrium is quickly established between Hl(g) and its decomposition products, H2(g) and Mg): 2 HKgl Q H2(g) + 12(8) The equilibrium constant at 1107 K is 0.0259, and the total pressure at equilibrium is observed to equal 6.45 atm. Calculate the equilibrium partial pressures of each substance. Problem #2 (7 marks! Stearic acid dimerizes when dissolved in hexane: 2 C17H35COOH(hexane) ¢> (C17H35COOH)2(hexane) The equilibrium constant for this reaction is 2900 at 28°C, but drops to 40 at 48°C. Estimate AH° and A80 for the reaction. Problem #3 (I 6 marksz Suppose 60.0 g of hydrogen bromide, HBr(g), is heated reversibly from 300 K to 500 K at a constant volume of 50.0 L and then allowed to expand isothermally and reversibly until the original pressure is reached. Sketch a P vs V graph for the process. Using Cp(HBr(g)) = 29.1 J/K, find AE, q, w, AH and AS for this process. Assume that HBr is an ideal gas under these conditions. Problem # 4 (12 marks! A sample containing 50.0 mL of 0.100 M aqueous solution of chloroacetic acid, CH2C1COOH (Ka = 1.4 x 104), is titrated with a 0.100 M NaOH solution. Calculate the pH at the following stages in the titration. o 0.00 mL of NaOH has been added 0 25.0 mL of NaOH has been added 0 50.0 mL of NaOH has been added 0 and 55.0 mL of NaOH has been added. 132] Midterm Examination — Equations and Data R = 8.314 J/mol.K = 8.314 kPa.l/mol.K = 0.0821 atm.L/mol.K ST P = standard temperature and pressure = 273.2 K and 101.3 kPa SA TP = standard ambient temp. and press. = 298 K and 100.0 kPa E uations or mdin AE AH and w 0 AB = q + w (special case AE = qv); AH = AE + APV (special case AH =qp) For isothermal processes 0 W = —nRTln(V2/V1) = -nRTln(P1/P2) (reversible); W = -APV (irreversible) For adiabatic processes TlVlY'l = Tszy'] ; P1V17 = P2V2Y where y = c (reversible) \ O < AE=nchT=w cp—CV=R AH = AE + APV = AE + (P2V2 — PIVI); AH = ncpAT Equations for finding AS In general, AS = qm/T; ASvap = AHvap/Tb; ASvap = 88 J/mol.K (Trouton’s rule) Entropy, Enthalpy and Free Energy Changes for Individual Substances AS = ncpln(T2/T1); AS = ncvln(T2/T1); AS = ann(V2N 1) and AS = ann(P1fP2) constant T ASM, = ASWS + ASS”; AG = nRTln(P2/P1) Changes Occurring During Reactions AXmamon = ZAXdproducts) — ZAXKreactants) where X =H or G ASmamon = 28(products) — 28(reactants) AGsys = AHsys — TASSyS = -RTan (at equilibrium) ln(K2/K1) = -AH°/R[1/T2 — l/Tl] (van’t Hoff equation) Engine Efficiency (8) = net work out/heat in 2 ' Wnet/qin = (Th — Tc)/Th (Carnot cycle only) Eqilibrium pH = -log[H+]; pOH = -log[OH']; pH + pOH =14; pKa = -log(Ka) pH = pKa + log[salt]/[acid]; kw = 1.00 x 10'14 Ovnméncdazé x5. anvauéOa. £3588 ._ .220 22.... 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Midterm Exam - QUEEN’S UNIVERSITY FACULTY OF APPLIED...

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