**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: C_{P} = - T·(∂^{2}G/∂T^{2})_{P,n}

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

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

• Isothermal compressibility: κ = - V^{-1}·(∂^{2}G/∂P^{2})_{T,n}

• Bulk modulus: B = 1/κ

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