The thermodynamic state of a system is defined by a set of state variables (properties) whose combination uniquely defines the present condition or state of the system.
States variables do not depend on the path taken to reach their current value. State variables can be measured at a specific instant of time. Examples of state variables include temperature, pressure, density, internal energy, density or specific volume, and enthalpy.
An equation of state is an equation that relates various state variables. An example of an equation of state is the ideal gas law that relates pressure, temperature, and specific volume. The values of state variables for a specific thermodynamic state can be found in the thermodynamic tables included with most textbooks.
Concepts associated with thermodynamic states and equations of state.