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Free Energy & Chemical Thermodynamics Flashcards

(11 cards)

1
Q

Free Energy

A

Energy available for work

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2
Q

Enthalpy

A

Energy of system plus work needed to make room for it.

H = U + PV

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3
Q

Helmholtz Free Energy

A

System with constant temperature and volume.
Total energy needed to create the system minus the heat you can get for free from environment at temperature T.

F = U - TS

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4
Q

Gibbs Free Energy

A

System with constant P and T.
System’s energy minus the heat term plus the atmospheric work.

G = U - TS + PV

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5
Q

Change in Helmholtz Free Energy

A

ΔF = ΔU - T ΔS = Q + W - TΔS

At constant temperature:
ΔF <= W

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6
Q

Change in Gibb’s Free Energy

A

ΔG = ΔU - T ΔS + P ΔV = Q + W - T ΔS + P ΔV

So ΔG = ΔH - T ΔS

W = -P ΔV + Wother

So at constant T, P:
ΔG <= Wother

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7
Q

Thermodynamic Potentials

A

U, H, F, and G

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8
Q

Thermodynamic Identities Given Enthalpy & Free Energy

A

Enthalpy:

dU = TdS - PdV + udN
dH = dU + PdV + VdP

dH = TdS + VdP + udN

Helmholtz Free Energy:

dF = dU - TdS - SdT
dF = -SdT - PdV + udN

Gibb’s Free Energy:

dG = dU + PdV - TdS
dG = -SdT + VdP + udN

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9
Q

Free Energy as a Force Toward Equilibrium
Relationship between:

  1. Entropy, Volume, Energy
  2. Helmholtz Free Energy, Temperature, Volume
  3. Gibb’s Free Energy, Temperature, Pressure
A
  1. At constant energy and volume, entropy tends to increase.
  2. At constant temperature and volume, Helmholtz free energy tends to decrease.

dStotal = dS - 1/T dU = -1/T(dU-TdS) = -1/T dF

  1. At constant temperature and pressure, Gibb’s free energy tends to decrease.

dStotal = dS - 1/T dU - P/T dV = -1/T(dU-TdS +PdV) = -1/T dF

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10
Q

Gibb’s Free Energy & Chemical Potential

A

If you add one particle to a system, holding the temperature and pressure fixed, the Gibbs free energy of system increases by u.

u = (dG/dN) T, P

G = Nu
(u is the Gibbs free energy per particle)

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11
Q

Extensive versus Intensive Properties

A

If a quantity doubles when you double the # of particles, it is an extensive quantity.

Extensive: V, N, S, U, H, F, G, mass
Intensive: T, P, u, density

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