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McGILL UNIVERSITY FACULTY OF SCIENCE CHEMISTRY 203 MIDTERM EXAM (2 or 3HR) Examiner: Dr. W.C. Galley Nov. 12, 2007 6:00-8:00 PM, or 6:00-9:00 PM INSTRUCTIONS TO STUDENTS 1. The following options exist for this exam: Option I: answer the 5 questions in Part I only, 2 hours, covers new material, 20% of final grade. Option II: answer the 5 questions in Part I, and in addition, the 3 questions in Part II which review work covered on the first exam. The exam is 3 hours and will count for 30% of the final grade and 10% from the first exam. 2. Answer all questions in a McGill exam booklet. You may keep the exam paper. 3. The total value of Part I is 50 marks, Part II is 25 marks. The marks for each question appear in the left hand margin. 4. There are 3 pages to the examination not including the title and data pages. 5. Calculators without alphanumeric memory and a French-English dictionary are permitted. 6. No other external information, such as pages of formulae, is permitted. 7. If you anticipate that you might appeal some aspect of the marking please write in pen. CONSTANTS R(gas constant).......................................................................8.314 J mol-1K-1 -1 -1 ...................................................................0.082 l atm mol K No(Avogadro’s number)…………………………………6.02x1023 mol-1 DATA Standard Heats of Formation (kJ mol-1) and Absolute Entropies (J mol-1K-1) at 298K H o f C(g) H(g) O(g) H2(g) NH3(g) N2(g) H2O(g) H2O( ) (CH3CH2)2O 718.4 218.0 - So - - 46.1 -241.8 -285.8 -252.7 161.1 130.6 192.5 191.5 188.4 69.9 For ATP hydrolysis: Ho = -24.2 kJ mole-1, So = 22.4 J mol-1K-1 between 20 → 37oC Bond Energies (kJ mol-1) EC-H EC-C EC-O For H2O: 411 348 332 CP( ) = 75.3 J mol-1 K-1 C( ) = 4.183 kJ kg-1K-1 CP(ice) = 38.0 J mol-1K-1 Hofusion(273K) = 5.9 kJ mol-1 Hovap(298K) = 44.0 kJ mol-1 QUESTIONS Part I 1. From the species listed below: O2(g), C2D4(g), CO(g), 40Ar(g), Br2(g), HBr(g), C4H10(g), H2O(g) Select, and justify, the one that would display: i) ii) iii) iv) v) the lowest STran the highest STran the lowest Svibr. the highest Svibr the lowest Soverall (5) 2. DSC curves obtained with solutions of a globular protein and a small DNA appear in the figure below. These solutions freeze at -4oC. From the data provided: (a) Compute Hoden , Soden , Goden , and the fraction of the protein that is the denatured state at equilibrium for the 2 systems at 37oC, and at -3oC before the solutions freeze. (15) (b) Comment on the relative stability of the native structure in the 2 systems and whether cold denaturation had occured in either case. 3. An irreversible process occurs in Step 1. in the weight and/or elastic system hidden in the box below. The process takes the system to equilibrium at a temperature T1. The temperature is then raised to T2.with the system remaining at equilibrium (10) (a) From the responses shown above make a sketch (croquis), or describe (or both) the system and processes that occur inside in Step 1. and 2. Justify. (b) Would Ssurr be 0 , pos. or neg. for the irreversible in Step 1, ? Justify. (c) Which of the following molecular processes would be analogous to the weight/elastic process in part (a). Justify i) ii) iii) iv) H2(g) + ½ O2(g) → H2O(g), Q = 1.0, T = 298K H2O( )→H2O( g ), Q = 1.0, T = 383K denDNA → natDNA, Q = 1.0, T = 310K glucose (0.1 M) → glucose (0.01 M), i.e. Q = 0.1, T = 298K 4. A two-particle gas undergoes the transitions from state I state II shown below: (a) Indicate the type of process, or processes, that would be involved in the transitions illustrated in i) and ii). Write S for these transitions in terms of the Boltzmann expression: S = knw 2 w1 . Assume the particles are indistinguishable. (10) (b) Write an expression for S for transition ii) assuming 1 mole of particles was involved. 5. Calculate S when 40g of ice at -20oC are added to 40g of H2O( ) at 80oC in a Dewar flask. The system comes to equilibrium with 4.0g of ice and 76g of H2O( ) (10) remaining in the flask. ____________________________________________________________ Part II 6. From data at the front of the exam calculate H of O(g) and the O=O bond energy. Point out any assumptions involved in the calculations. (12) 7. (a) The hydrolysis of a sample of a 0.25M solution of phosphoenolpyruvate (PEP) to yield pyruvate (Pyr) and phosphate is catalyzed with an enzyme in a small adiabatic calorimeter. The temperature of the aqueous solution changes from 23.4 → 27.4oC during the reaction. Calculate the Hhydrolysis per mole of PEP. (8) (b) In a reaction catalyzed by pyruvate kinase the conversion of phosphoenolpyruvate → pyruvate is coupled to the formation of ATP: PEP + ADP → Pyr + ATP Calculate the fraction of the Hhydrolysis determined for PEP in part (a) that is captured in the formation of ATP in the reaction above. (Assume the Hhydrolysis determined for PEP is essentially that under standard conditions (H ohydrolysis) . The equation below is for information only, not required ). 8. Match the chemical species in the left-hand column with the CP values in the righthand column and briefly justify. (5) CP(J mol-1K-1) Ne(g) C6H6(g) Br2(g) D2(g) C(gr) 29.1 8.5 81.7 20.8 36.0