090206_lecture11

090206_lecture11 - Physical Chemistry I for Biochemists...

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1 Physical Chemistry I for Biochemists Chem340 Lecture 11 (2/6/09) Yoshitaka Ishii Ch3.4-3.6 (skip printing p2-3 if you have lec. note 10) Integral HW4 Announcement • Answer for HW3 is up at the website • For Exam 1, the area to be covered is Ch1-3 & Ch4.1-2 (solve the example problem in p67). • Review class for Exam 1 for next Wednesday • HW4 needs some corrections. Please download a file named “090202_Homework4_rev1.pdf”.
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2 3.2 Dependence of U on V and T • U varies by changing V and T as dT T U dV V U T V dU V T + = ) , ( v V V C dT Dq T U = P T P T V U V T = To be derived in Sec. 5.3 dT C dV P T P T T V dU V V + = ) , ( For an ideal gas, this term is zero. 3.4 Variation of Enthalpy with Temperature at Constant P Recap of the relationship between Δ U and H for an ideal gas. H U +PV Æ Δ H = Δ U+ Δ (PV) Namely, Δ H = Δ U+ Δ (nRT) Æ Δ H = Δ U+ nR Δ T For ideal gas , Δ U = C V Δ T (C v is const in most cases). Æ Δ H = C V Δ T + nR Δ T=(C V + nR) Δ T =C p Δ T
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3 Enthalpy for general case • For Reversible Process (P = Pext) at Constant P , •d U = D q p –P ext dV = Dq p –PdV Æ Dq p = dU + PdV = dH Æ q p = Δ H (cf. qv = Δ U ) • (Not restricted to ideal gas; correct for a closed system) Δ U and Δ V for Vaporization and Fusion • Vaporization: liquid Æ gas • Fusion: solid Æ liquid Vaporization/Fusion occurs at a constant T if a system is held at a constant P. Δ U vaporization = Δ H vaporization -P Δ V vaporization Δ V vaporization = V gas –V liquid ~V gas >> 0 Æ Δ U vaporization < Δ H vaporization Δ U fusion = Δ H fusion Δ V fusion ~ Δ H fusion Δ V fusioin = V liquid solid ~0
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4 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 at 200K? 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 =
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This note was uploaded on 10/11/2009 for the course CHEM 340 taught by Professor Staff during the Spring '08 term at Ill. Chicago.

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090206_lecture11 - Physical Chemistry I for Biochemists...

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