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090126_lecture6 - Physical Chemistry I for Biochemists...

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1 Physical Chemistry I for Biochemists Chem340 Lecture 6 (1/23/09) Yoshitaka Ishii Ch. 2 (Skip printing p2-4 if you have lecture note 5) Announcement Key for HW1 is at the web site Quiz 1 this Friday (15 mins) Multiple choice but including calculations Topics up to the materials covered Wednesday 60-70% of questions from materials in HW1 & HW2 (do not expect the same ones)
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2 Ch. 2 First law of Thermodynamics: The internal energy, U, of an isolated system is constant. Δ U system = - Δ U surrounding In other words, if the surrounding exchanges energy with the system, the total energy of the surrounding and the system should not change. 0= Δ U Total = Δ U system + Δ U surrounding In a closed system : - Δ U surrounding = q(heat) + w(work) Δ U = q + w 2.2 Work Definition: Any quantity of energy that flows across the boundary between the system and surrounding by a force The work dW is done by moving a object through a small distance d L with force F as dW = F d L =FdL cos θ θ F dL L F dL F w Δ = = If θ =0
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3 Work by pressure ) ( ) ( V d P dz A P dz A P dL F w external external external = = = = Pressure: P = F/A, where A is area Æ F = P external A The work done by the system: A dz Note: In general, P external P system P ex ) ( ini fin external V V P w = If P external is constant Æ The sign of w Initial Initial Final Final W > 0 W < 0 Δ U = w > 0 Δ U = w < 0 P’ i V’ i P’ f V’ f P i V i P
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