Thermodynamic equations of state for fluids

Thermodynamic properties such as density, heat capacities, speed of sound, enthalpy, entropy, and other properties, can be calculated from a single thermodynamic equation of state in the case of pure fluids. Equation of state representing Helmholtz free energy provides those property values accurately in wide gaseous, liquid, and supercritical phases even at high temperatures and pressures by only differential procedures, which is sometimes called as fundamental equation of state. For many important fluids like water, air, carbon dioxide, ammonia, methane, isobutane, methanol, and hydrofluorocarbons (HFCs), the fundamental equations of state have already been established. This article introduces these fundamental equations of state and the background of them. Some latest aspects obtained in our group on thermodynamic equations of state are also introduced.