An equation of state relates intensive properties of a pure substance.
- For example, the ideal gas law, , is an equation of state
It can take the following forms:
- Algebraic (ideal gas law – may only be valid for certain conditions/assumptions)
- Graphical (P-v-T surface)
- Tabular (Property tables)
For example, we can define for a pure substance undergoing a quasi-equilibrium process to use in: .