090128_lecture7

090128_lecture7 - Physical Chemistry I for Biochemists...

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1 Physical Chemistry I for Biochemists Chem340 Lecture 7 (1/28/09) Yoshitaka Ishii Ch. 2 (Skip printing p2-3 if you have lecture note 6) Announcement • Does any of you want to form a study group for this class? • HW3 is up at the web site. If you have a trouble about the differential, read Appendix A.2 (A.2.1-A2.3). Partial derivatives are summarized in A.6. I plan to cover the subjects on Friday.
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2 2.5 State Functions and Path Functions • An alternate statement of first law: Δ U is independent of the path between the initial and final states . Δ U only depends only on the initial and final states as Any function that satisfies this condition is called a state function . ini fin U U U U dU U fin ini = = Δ d U is called an “ exact differential ”, the integration of which (U) is a state function. ( D q is not an exact differential). Work and Heat Depends on a “Path” of P, V, T • Assume that (P, V, T) is changed as follows: State 1 State 2 State 3 (P 1 , V 1 , T 1 ) Æ (P 2 , V 2 , T 2 ) Æ (P 3 , V 2 , T 3 ) W = -P ext ( V 2 - V 1 ) Æ W depends on the weight Δ U(1 3) = w +q Æ q = Δ U-w Q. Does q depend on weight?
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3 What Defines State Functions? • The state of a single phase system at fixed composition is defined by any two of P, T,V. Æ U is defined as U(T, P), U(P, V), or U(V, T) 0 0 0 0 0 0 0 = = = Δ ) , , ( ) , , ( V T P U V T P U dU U ini fin Cyclic Integral 0 0 0 0 0 0 0 = = = Δ ) , , ( ) , , ( V T P X V T P X dX X ini fin For any state function X Work and Heat Are “Path Functions” (not “State Function”)
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090128_lecture7 - Physical Chemistry I for Biochemists...

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