Tutorial 4 Notes - CHM2132 Tutorial notes for Oct 2nd and...

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CHM2132 Tutorial notes for Oct 2 nd and 9 th . 1) Calculate the increase in entropy when 3.50 mol of a monatomic perfect gas with C p,m =5/2 R is heated from 250 K to 700 K and simultaneously expanded from 20.0 L to 60.0 L. There are two equivalent reversible paths that we can use: We are given: n = 3.5 mol, C p,m =5/2R, T 1 = 250 K, T 2 = 700 K , V 1 = 20 L, V 2 = 60 L From our analysis of the p-V diagram the reversible heat for this process can be calculated with a reversible isothermal expansion to 60 L followed by a reversible constant volume heating process. The equation for the heat of a reversible isothermal expansion: Since 0 U ! = q w pdV ! = " = Substitute in the ideal gas equation: nRT q dV V = Since this is the equation for the heat from a reversible process we can substitute this equation into the equation for entropy: isothermal expansion 2 1 2 1 ln rev V V q S T nR dV V V nR V " = = # $ = % ( ) ) The equation for heat of reversible heating to 700 K: Since dV = 0 , V m dU q C dT = = (Remember it is always UV, that is U is calculated using C V ) Substitute into the equation for entropy:
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2 1 2 1 2 , 1 ln ln rev heating T V T V V m q S T C dT
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This note was uploaded on 01/22/2011 for the course CHM 2132 taught by Professor Giorgi during the Fall '08 term at University of Ottawa.

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Tutorial 4 Notes - CHM2132 Tutorial notes for Oct 2nd and...

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