Common 'Energies'
- Internal Energy: U + Q + W
Checks the gain/loss from any change in the system's internal state.
- Helmholtz Energy: A = U - TS
Thermodynamic potential, measure of useful work. Obtainable from a closed thermodynamic system at constant T & V.
- Gibbs Energy: G = U + PV - TS = A + PV
Thermodynamic potential giving the maximum amount of reversible work doable by a system at constant temperature and pressure.
Strictly speaking, all of these should probably factor in the particle number and chemical potential,

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Ensembles:
- Canonical Ensemble:
T=const, sytem in contact with thermal bath, energy flows between but is in thermal equilibrium; particles are stuck but heat flows.
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(138) |
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(139) |
- Microcanonical Ensemble:
Isolated system - statistical ensemble representing possible states of equal energy, multiplicity
- Grand Canonical Ensemble:
System in contact with a heat bath and particle bath. Particles and energy can be swapped, with an equilibrium T.
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(140) |
G. partition function:  |
(141) |
Equipartition Theorem
At temperature T, the average energy of a quadratic degree of freedom
Entropy, Fluctuations, Heat Capacity
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(144) |
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(145) |
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(146) |
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(147) |
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(148) |
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(149) |
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(150) |
Blackbody Radiation
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(151) |
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(152) |
From here on,  |
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(153) |
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(154) |
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(155) |
With a 2 added somewhere along the way to properly count polarization modes.
Fugacity, q-potential, average particle number:
Subsections