The Gibbs energy G can be decomposed as G id + G res , the sum of the ideal gas part and the residual part. The residual Gibbs energy, G res (T, P ), at a given temperature and pressure captures all effects from all types of intermolecular interactions, along with their volume, entropy, and pressure dependencies. All thermodynamic properties can be derived from residual Gibbs energy G res (T, P ). The response functions of G res (T, P ), i. e., the first, second, and mixed derivatives of G res (T, P ) with respect to temperature and pressure, are sufficient to mathematically express the thermodynamic properties exhibited by a fluid, unless auxiliary forces such as electrical fields are introduced.