Second Law, Heat Engines and Entropy

Name: Second Law, Heat Engines and Entropy
Author: StemPy Lab

Heat flows from a hot body to a cold one by itself, and never the other way. A car engine wastes most of the energy of its fuel. In this course we state the second law of thermodynamics, we find the efficiency of heat engines and the coefficient of performance of refrigerators, we learn why the Carnot engine is the best possible, and we meet entropy, which tells us the direction in which changes happen.

3 lessons, about 1 h 15 min3 simulations12 problems6 practice questionsPython in every lesson

Created by StemPy Lab

Course outline (3 lessons)

Lesson 1about 25 min
Cyclic processes, the second law and reversibility
In a cyclic process a gas comes back to its start, so $\Delta U = 0$ and the net heat taken in equals the net work, the area of the loop. The second law says no engine can turn all the heat it takes in into work (Kelvin-Planck), and no refrigerator can move heat from cold to hot with no work (Clausius). A reversible process is slow, with no friction and no heat flow across a gap in temperature; every real process is irreversible.
1 simulation2 practice questions1 Python program4 problems1 Python lab
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Lesson 2about 25 min
Heat engines, refrigerators and the Carnot engine
A heat engine takes heat $Q_h$ from a hot reservoir, does work $W$ and gives heat $Q_c$ to a cold one; its efficiency is $\eta = \dfrac{W}{Q_h} = 1 - \dfrac{Q_c}{Q_h}$ . A refrigerator uses work to move heat from cold to hot, with $\text{COP} = \dfrac{Q_c}{W}$ . The reversible Carnot engine, two isotherms and two adiabats, is the best possible: $\eta = 1 - \dfrac{T_c}{T_h}$ , with temperatures in kelvin.
1 simulation2 practice questions1 Python program4 problems1 Python lab1 question set
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Lesson 3about 25 min
Entropy and the direction of change
Entropy $S$ tells which way things happen by themselves. Heat $Q$ taken in reversibly at a temperature $T$ raises it by $\Delta S = \dfrac{Q}{T}$ ; for a gas at a steady temperature $\Delta S = nR\ln\dfrac{V_2}{V_1}$ . The second law says the total entropy of an isolated system never falls: it rises in every real process and stays the same only in a reversible one.
1 simulation2 practice questions1 Python program4 problems1 Python lab1 note
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Second Law, Engines and Entropy: Mock Exam

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Second Law, Heat Engines and Entropy

Course outline (3 lessons)

Cyclic processes, the second law and reversibility

Heat engines, refrigerators and the Carnot engine

Entropy and the direction of change

Test Your Learning

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