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# lecture41 - VIII Entropy 1 Macroscopic definition of...

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VIII. Entropy T dQ dS for a reversible process at constant T dQ is path dependent dS is path independent S is function of state S is additive function T dQ dS for any process (including irreversible) For closed, isolated system (dQ = 0): 0 dS 2.The second law of thermodynamics any reversible cycle: Δ S=0 any irreversible process in closed isolated system: Δ S>0 1. Macroscopic definition of entropy

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Example 1: This P-V diagram represents a system consisting of a fixed amount of ideal gas that undergoes three different processes in going from state A to state B. Rank the change in entropy of the system for each process. V State A I P State B 2 3 Δ S 1 = Δ S 2 = Δ S 3 = S B -S A The same as: Δ T 1 = Δ T 2 = Δ T 3 = T B -T A Δ U 1 = Δ U 2 = Δ U 3 = U B -U A Example 2: Which of the following statements is false? A. The change of entropy in a cyclic process is zero B. The change of entropy for any adiabatic process is zero C. The change of entropy for any isothermal process is zero D. Entropy for a closed, isolated system is constant E. Entropy of a system can decrease
Example 3: 50.0 kg of water is converted to ice at 0.0ºC. What is the change in entropy of water? m = 85.0 kg T = 0.0ºC L = 334*10 3 J/kg Δ S - ?   K kJ K kg J kg S T mL T Q S / 61 273 / 10 334 0 . 50 3 Example 4: The isolated system is 50.0 kg of ice at 0 ˚ C plus the temperature reservoir at slightly above 0 ˚ C that is used to melt the ice.

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## This note was uploaded on 10/21/2010 for the course PHYS 221 taught by Professor Herrera-siklody during the Fall '08 term at Iowa State.

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lecture41 - VIII Entropy 1 Macroscopic definition of...

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