090208_lecture12

090208_lecture12 - Physical Chemistry I for Biochemists...

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1 Physical Chemistry I for Biochemists Chem340 Lecture 12 (2/9/09) Yoshitaka Ishii Ch3.5-3.7 (skip printing p4-6 if you have lec. note 11) Integral HW4 Announcement • HW4 is due this Wednesday. Answers for HW4 will be uploaded after the Wednesday. • For Exam 1, the area to be covered is Ch1-3, 4.1-4.2 (For Ch4.1 understand Fig. 4.1) • Review class for Exam 1 for next Wednesday • HW4 P2.31 & Question 3 needs additional correction (as announced in the Discussion class). P2.31: B = 2.00 × 10 –28 J m –1 Æ B = 2.00 × 10 –28 J m All the answers at the back are correct for HW4
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2 HW4. Q3 3. Assuming that dU is an exact differential, show dH is also an exact differential for P and V. (Hint: Define dU as dU = f(P,V)dP + g(P, V)dV & use ( f/ V) P = ( g/ P) V ). You can also use dH = d(U + PV) = dU + P dV + VdP. Heat Capacity C V of Various Gas 2 3 R dT dE trans = () 2 5 R dT E E d rot trans = + Q. What defines C V for C 2 H 4 & CO 2 at 200K? Hint: R ~ 8 JK -1 mol -1 R dT E E d rot trans 3 = +
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3 ( U/ V) T for van der Waals Gas Example Problem 3.4 (text p51) For a gas described by the van der Waals eq of state, P = RT/(V m - b) –a/V m 2 . (a) Calculate ( U/ V) T using ( U/ V) T = T ( P/ T) V –P. (b) Derive an expression for the change in internal energy, in compressing a van der Waales gas from an initial molar volume VM to a final molar volume V m at constant temperature. dV P T P T U Vfin Vini V T = Δ (a)vdW eq: P = RT/(V m - b) –a/V m 2 (b) Solution (correction) 2 2 m V m m V T V a P b V RT P T V a b V RT T P T P T V U m / ) ( / ) /( = = = = {} = = = = Δ fin m ini m V V m m Vmfin i V m m Vmfin i V V Tm V V a V a dV V a dV P T P T U fin m ini m 1 1 2 min min / Æ This term represents inter-molecular interaction
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4 3.4 H as a function of P & T • H varies by changing P and T as When dP = 0 (& P = P ext ) dT T H dP P H T P dH P T + = ) , ( dT T H dH Dq P p p = = P P P C dT Dq T H = P T T V T V P H = When V = kT Æ This term is zero
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090208_lecture12 - Physical Chemistry I for Biochemists...

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