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

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