11/12.3 Entropy and the Second Law of Thermodynamics

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Entropy and the Second Law of Thermodynamics

ENTROPY AND THE 2ND LAW OF THERMODYNAMICS
Entropy Entropy is related to disorder or randomness.
It is a measure of disorder.
2nd Law of
Thermodynamics
For a spontaneous process, the entropy of the universe increases.
For a spontaneous process, ΔSuniverse > 0.
For a spontaneous process, ΔSsystem + ΔSsurroundings > 0.
Entropy Change ΔS = qrev / T
Isothermal
Expansion of an
Ideal Gas
ΔS = nR ln Vf / Vi
Entropy Change
Upon Heating
ΔS = nC ln Tf / Ti
Entropy S = kBlnW            W = # microstates            kB = 1.38 × 10-23 J / K

Heat Engines and Thermal Efficiency

HEAT ENGINES AND THERMAL EFFICIENCY
Work Done by a
Heat Engine
weng = |qh| - |qc|
Thermal Efficiency
12.3 heat engines2

Carnot Cycle

CARNOT CYCLE
1. Isothermal
    Expansion
q = nRThln V2 / V1 ΔS = nRln V2 / V1
2. Adiabatic
    Expansion
q = 0 ΔS = 0
3. Isothermal
    Compression
q = nRTcln V4 / V3 ΔS = nRln V4 / V3
4. Adiabatic
    Compression
q = 0 ΔS = 0
Thermal Efficiency
Carnot Cycle
η = 1 - |qc| / |qh| = 1 - Tc / Th
12.3 carnot cycle