Lecture7_drobny - Lecture 7: Thermo and Entropy Reading:...

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Lecture 7: Thermo and Entropy • Reading: Zumdahl 10.2, 10.3 • Recommended Problems: 10.10.21, 10.23, 10.25, 10.27 • Outline – Isothermal processes – Isothermal gas expansion and work – Reversible processes
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What the Second Law Does • Defnes a new State Function Called “Entropy” S. • Predicts the ‘spontaneous’ direction ±or physical and chemical process based on how the entropy o± the universe changes. • Designates the upper limit ±or the e±fciency o± heat machines…how much work can be extracted ±rom heat trans±er.
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How to Understand Entropy by Building a Heat Engine
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Isothermal Processes • Recall: Isothermal means Δ T = 0. • Since Δ E = nC V Δ T, then Δ E = 0 for an isothermal process. • Since Δ E = q + w: q = -w (isothermal process)
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Example: Isothermal Expansion • Consider a mass connected to a ideal gas contained in a “piston”. Piston is submerged in a constant T bath such that Δ T = 0.
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Isothermal Expansion (cont.) Initially, V = V 1 P = P 1 Pressure of gas is equal to that created by mass: P 1 = force/area = M 1 g/A where A = piston area g = gravitational acceleration (9.8 m/s 2 )
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Isothermal Expansion (cont.)
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This note was uploaded on 01/18/2012 for the course CHEM 152A taught by Professor Chiu during the Fall '12 term at University of Washington.

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Lecture7_drobny - Lecture 7: Thermo and Entropy Reading:...

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