Classical thermodynamics, heat transfer Definition

Thermodynamic state

Definition

Let $\Sigma$ be a thermodynamic system. A state variable of $\Sigma$ is a macroscopic quantity of $\Sigma$ that can be measured at a given time. Examples are pressure, volume, temperature and amount of substance. The thermodynamic state of $\Sigma$ at a given time is the list of values of its state variables at that time. For a system in equilibrium, the state is fixed by finitely many independent state variables. All other state variables are then functions of them.

Remarks

For a fixed amount of a simple fluid in equilibrium, the pressure $p > 0$ and the volume $V > 0$ determine the state. The temperature is then a function of $(p, V)$ , given by the equation of state. The full list of positions and velocities of the molecules is not a thermodynamic state: it is a microscopic state, and many such microstates correspond to the same thermodynamic state. The thermodynamic state is also called the macrostate.

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Thermodynamic system concept
Thermodynamic state definition

Tag	`M0VVMN6594`
URI	`m2://M0VVMN6594`
Kind	definition
Writing	W0 stub
MSC	80A05, 80A10
Defines	Thermodynamic state
Uses	Thermodynamic system
Changed	3 November 2026

Thermodynamic state

Definition

Remarks

Reading path

Further reading

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