MidtermExam_withSolutions - QUEEN’S UNIVERSITY FACULTY OF...

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Unformatted text preview: QUEEN’S UNIVERSITY FACULTY OF APPLIED SCIENCE APSC 132J Chemistry and Materials Midterm Examination May 4, 2001 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: ten short knowledge questions 9 marks Part B: ten short calculations problems (2 marks each) 26 marks Part C: two major problems [varied weighting! 35 marks Total 70 marks The answers to PartsA and B will be placed on a computer-marked sheet. To answer these questions: C You must use a soft-lead pencil (H3 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. 4 Write and code you name and student number on the answer sheet in the upper left—hand corner. 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. c. An isothermal expansion of an ideal gas from 1L to 10L against an opposing force of 5 atm d. An isothermal reversible expansion of an ideal gas from 11. to 10 L. The equilibrium constant for A + B ¢i> C is 0.123. What is the equilibrium constant for 2C<=> 2A + 2B? a. 8.13 d. 16.3 b. 0.123 C. 66.1 Consider the equilibrium system, A(g) + B(g) 61> C(g) + D(g). At 25°C, the value ofK is 1.2 x 10'3. At 50°C, the value of K is 3.4 x 10". The reaction is: a. exothermic b. endothermic c. more information needed d. impossible to tell Calculate the pH of a 0.02 M solution of KOH. a. 1.7 b. 2.0 c. 12.0 d. 12.3 Calculate the pH in a solution of 1.0 M HZA. K211 :1.0 x10'6;Ka2 =1.0 x1010. a. 8.00 b. 7.00 c. 6.00 d. 3.00 For a particular process, q = 20 kJ and w = 15 kJ. Which statement is true? a. Heat flows from the system to the surroundings. b. The system does work on the surroundings. c. AE : 35 k] d. All of the above are true, If a student carried out an endothermic reaction in a reaction vessel surrounded by water and placed inside of a calorimeter, how would the calculated value of AH differ from the actual value if the heat exchanged with the calorimeter was not taken into account? Only the heat exchanged with the water was accounted for. a. The calculated value would be more negative because the calorimeter always absorbs heat from the reaction. b. The calculated value would be less negative because the calorimeter would absorb heat from the reaction. 0. The calculated value would be more positive because the reaction absorbs heat from the calorimeter. d. The calculated value would be less positive because the reaction absorbs heat from the calorimeter. 8. Consider the numbered processes. 1.A-)2B AHI 2.B-)C+D AH2 3.E-)2D AH3 Find AH for the process A -) 2C + E 21. AH] + AHZ + AH3 b. AHl + AH2 C. AH1+ AH; - AH3 d. AHl + 2AH2 - AH3 Consider the equilibrium system PC13(g) + C12(g) ¢i> PC15(g). When some C12(g) is added at constant volume and temperature, the ratio of partial pressure of PC15 to the partial pressure of PC13 a.increases b. decreases c. stays the same d. more information needed Part B: Each correct answer is worth 2 marks 10. 11. 12. 13. 14. 15. 16. In an irreversible isothermal process, the pressure on 1.00 mol of an ideal gas changes from 2.50 atm to 6.50 atm at 27°C. Q is equal to: (Note: 1 L.atm = 101.3 J) a. —2.38 U b. 2.38 k] c. 3.99 kl d. —3.99 H For a weak acid HX, the pH of a 0.10 M solution is 5.83 at 25°C. What is AGO for the dissociation reaction at 25°C? a.—61k.l d. 61 k] b. —30 k] c. 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 c. 1.74 atm d. 0.574 atm For the reaction, 3m®+M®¢flNE® what is the relationship between Kc and Kp at temperature T? a. Kc = Kp b. Kp = Kc(RT)2 0. KC = Kp(RT)2 d. Kc = \le The pH ofa 0.010 M weak acid solution is 5.24. Calculate Ka for this acid. a. 3.3 x10‘9 b. 1.8 x10'6 c. 4.2 x 10'7 d. 9.6 x10'8 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 pH = 2.50? a. 1.6x 10'1 b. 2.0x 10'2 c. 7.8 x10‘2 d. 0.50 The pKa of HOCl is 7.5. Calculate the pH ofa 0.5 M solution of HOCl. a. 7.5 b. 6.5 c. 3.9 d. 10.1 17. 18. 19. 20. 21. 22. Calculate the pH ofa 0.20 M solution of NaC2H302. Ka for HC2H302 is 1.8 X 105. a. 4.98 b. 9.02 C. 5.44 d. 8.56 A calorimeter contains 150 g of water at 24.60 A 110 g block of molybdenum metal is heated to 100.00C and then placed in the water in the calorimeter. The contents of the calorimeter come to an average temperature of 280°C. What is the heat capacity per gram of molybdenum metal? Assume that no energy is lost to the calorimeter or the surroundings. The heat capacity of water is 4.18 J/g.K a. 0.27 J/g.K b. 0.064 J/gK c. 30 J/gK d. 15 J/g.K The heat of vaporization of rubidium is 69.0 kJ/mol at its boiling point (686°C). The process Rb(1) -) Rb(g) takes place at 1 atm and 686°C. ASSllr is equal to: a. —71.9 J/mol.K b. 101 J/mol.K c. 71.9 J/mol.K (1. W101 J/mol.K Consider the reaction CZHZ (g) + 2112 (g) <=> C2H6(g). AGOf Csz(g) 209.2 kJ/mol C2H6(g) -32.9 kJ/mol Calculate Kp at 298K for this reaction. a. 9.07 x101 b. 97.2 c. 1.24 x 103' d. 2.72 x 10‘“2 For the reaction 2 SOz(g) + 02(g) <1=> 2 803(g), AHD : -200 k] and A80 = —187 .l/K at 250C. Assuming that AH0 and A80 are independent of temperature, calculate the temperature at which Kp = 1. a. 970 K b. 1070 K c. 200 K d. 2070 K 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 270C. Calculate AS? a. 7.94 J/K b. 47.94 J/K c. 13.3 J/K d. —13.3 J/K Part C: This section of the examination is worth 35 marks. The questions in this section should be answered in the examination answer booklets. Problem # I (14 marks) A sample containing 50.0 mL of 0.100 M aqueous solution of chloroaeetic acid, CHgClCOOH (Ka = 1.4 x 104), is titrated with a 0.100 M NaOH solution. Calculate the pH at the following stages in the titration, and plot the titration curve showing pH vs mL of NaOH added. 0 0.00 mL of NaOH has been added 0 25.0 mL of NaOH has been added 0 50.0 mL ofNaOH has been added 0 and 55.0 mL of NaOH has been added. Problem #2 (7 marks} A system consists of a cylinder containing 8.0 L of an ideal gas at 25°C and at a pressure of 10.0 atm. The gas is allowed to expand isothermally and irreversibly against a constant opposing pressure of 5.0 atm until its pressure reaches 5.0 atm. Calculate the entropy changes in: a. the system b. the surroundings, and c. the universe for this process. Problem #3 (14 marks) 1.0 kg of $02, at a pressure of 2.00 atm and 300 K (state 1), is compressed adiabatically and reversibly to 400 K(state 2). This compression is followed by a reversible isothermal expansion to the initial pressure (state 3). The gas is subsequently cooled reversibly at this pressure to the initial conditions (state 1). [CI) : 0.609 kJ/kgK, CV : 0.479 kJ/kg.K. R = 130 J/kg.K] a. Draw the cycle in a P — V diagram. b. Calculate the heat and work for the three steps in this cycle. 0. Calculate the total heat and work for the cycle. 132] Midterm Examination — Equations and Data R = 8.314 J/mol.K = 8.314 kPa.l/mol.K = 0.0821 atm.L/mol.K S T P = standard temperature and pressure = 273.2 K and 101.3 kPa SAT P = standard ambient temp. and press. = 298 K and 100.0 kPa Equations for finding AEI AH, q and w 0 AB = q + w (special case AB = q”; AH = AE + APV (special case AH =qp) For isothermal processes 0 W = -nRTln(V2/V1) : -nRT1n(Pl/P2) (reversible); W : —APV (irreversible) For adiabatic processes T1V1Y‘1 = TZVZY‘I ; P1V]Y I PZVZy where y = c /cV (reversible) AB 2 chAT 2 w cp - CV = R AH = AE ‘i' APV : AE + (P2V2 —- PIVI); AH : ncpAT Equations for finding AS In general, AS : qm/T; ASWP : AHWP/Tb; ASvap = 88 J/m01.K (Trouton’s rule) Entropy, Enthalpy and Free Energ/ Changes for Individual Substances AS = ncpln(T2/T1); AS = ncvln(T2/T1); AS = ann(V2/V1) and AS = ann(P1/P2) constant T Astor : ASsys + Assur; : 11RT111(P2/P1) Changes Occurring During Reactions AXmaction = EAXf(_pr0ducts) — ZAX1(reactants) where X :H or G ASreaction = ZS(products) — ZS(_reactants) AGSVS = AHSyS — TASSys ' : —RT1nK (at equilibrium) ln(K2/K1) = -AH°/R[1/T2 — l/TI] (van’t Hoff equation) Engine Efficiency (8) = net work out/heat in : ' VVnet/qm : (Th — TC)/T11 (Carnot cycle only) Eqilibrium pH = -10g[H+]; pOH : —log[OH']; pH + pOH =14; pKa = -10g(Ka) pH = pKa +10g[salt]/[acidj; kw : 1.00 x 10'14 ZWV 2/? 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