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Glossary

Gibbs Energy

The Gibbs energy is a thermodynamic function of state defined by

G = H - T·S

where H is the enthalpy (Joules), T is the absolute temperature (Kelvins), and S is the entropy (Joules per Kelvin).

Once the Gibbs energy is known, all other thermodynamic properties can be derived. For example:

Entropy: S = - (∂G/∂T)P,n

Enthalpy: H = G - T·(∂G/∂T)P,n

Helmholtz energy: A = G - P·(∂G/∂P)T,n

Internal energy: U = G - T·(∂G/∂T)P,n - P·(∂G/∂P)T,n

• Volume: V = (∂G/∂P)T,n

• Heat capacity at constant pressure: CP = - T·(∂2G/∂T2)P,n

• Chemical potential (partial Gibbs energy): μ = (∂G/∂n)T,P

• Thermal expansion: α = V-1·(∂2G/∂T∂P)n

• Isothermal compressibility: κ = - V-1·(∂2G/∂P2)T,n

• Bulk modulus: B = 1/κ

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