Classical thermodynamics, heat transfer Definition

Thermodynamics

Builds on Thermodynamic system Thermodynamic state Thermodynamic equilibrium

Definition

Thermodynamics is the physical theory of macroscopic thermodynamic systems and of the exchanges of energy between them as heat and as work. In classical (equilibrium) thermodynamics:

Each system has equilibrium states.
Each equilibrium state is described by finitely many real state variables, such as volume, pressure, amount of substance and temperature.
The possible changes of state are restricted by the laws of thermodynamics, which are taken as postulates.

Remarks

A gas in a cylinder with a piston is a typical subject. Its equilibrium states are described by the pair $(p, V)$ of pressure and volume. Thermodynamics relates the heat and work exchanged when $(p, V)$ changes. The motion of a single molecule of that gas is not a subject of classical thermodynamics, because it is a microscopic description; it belongs to mechanics and to statistical mechanics. Non-equilibrium thermodynamics extends the theory to systems that are not in equilibrium.

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Tag	`V4ERH9VYBT`
URI	`m2://V4ERH9VYBT`
Kind	definition
Writing	W0 stub
MSC	80A05, 80A10
Defines	Thermodynamics
Uses	Thermodynamic system, Thermodynamic state, Thermodynamic equilibrium
Changed	3 November 2026

Thermodynamics

Definition

Remarks

Reading path

Further reading

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