Download doc 2007 midterm 2

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 = knw 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