Lecture 9 1-28-08 Entropy2

Lecture 9 1-28-08 Entropy2 - System and Surroundings for...

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System and Surroundings for Isothermal Gas Expansion/Compression

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The First Two Laws of Thermodynamics First Law E = q + w (Conservation of Energy) How do you derive it? How do you measure internal energy? Is it useful? Second Law S – q irr /T > 0 (Spontaneous) How do you derive it? How do you measure entropy? Is it useful?
Three Big Questions Isothermal Expansion and Compression 1. How do we calculate the entropy for the isothermal expansion and compression of a gas? T q S rev = Δ i f V V ln nR S Δ = i f rev V V ln nRT q =

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Question 2 • Expansion pathway and compression pathway are different. That’s what we mean by irreversible. Why does it take more work to irreversibly compress a gas than we get by expanding it ? Initial State High P Final State Low P Expansion, Low P EXT Compression, High P EXT
• How is heat transferred in an isothermal expansion/compression when T is constant? •S i n c e Δ E = 0, q = -w • In expansion, system does work by abosrbing heat from the surroundings • In compression, surroundings do work with heat from system.

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This note was uploaded on 08/06/2008 for the course CHEM 1B taught by Professor Watts during the Winter '08 term at UCSB.

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Lecture 9 1-28-08 Entropy2 - System and Surroundings for...

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