Equilibrium thermodynamics

Equilibrium thermodynamics describes systems in thermodynamic equilibrium through relations among macroscopic properties, without modeling the processes by which equilibrium is reached.

Thermodynamic equilibrium: A state in which a system has no macroscopic tendency to change and satisfies thermal, mechanical, and chemical equilibrium. It is the defining condition for states described by equilibrium thermodynamics.
Zeroth law of thermodynamics: The law stating that systems in thermal equilibrium with the same third system are in thermal equilibrium with each other. It establishes temperature as a consistent criterion for thermal equilibrium.
Phase equilibrium: A condition in which multiple phases coexist without net transfer of matter between them. Equilibrium thermodynamics determines when phases coexist and how their properties relate.
Nonequilibrium thermodynamics: The study of systems away from equilibrium, including transport and irreversible processes. Unlike equilibrium thermodynamics, it addresses gradients, flows, and dissipation.
Sadi Carnot: A French engineer whose 1824 analysis of heat engines established limits on their efficiency. Carnot's work helped reveal universal relations independent of engine design.
Thermodynamic state: A condition of a system specified by a set of macroscopic properties. Equilibrium thermodynamics represents systems through their states rather than their histories.
First law of thermodynamics: The conservation law that relates changes in internal energy to heat and work. It constrains energy changes between equilibrium states without specifying a process's detailed dynamics.
Phase diagram: A graph showing which phases are stable across conditions such as temperature, pressure, and composition. Phase diagrams summarize equilibrium predictions across changing external conditions.
Statistical mechanics: The framework that derives macroscopic behavior from statistical descriptions of microscopic states. It can provide microscopic explanations for equilibrium relations that this framework takes as macroscopic laws.
Rudolf Clausius: A German physicist who formulated the second law and introduced the concept of entropy. His formulations supplied central principles for equilibrium descriptions.

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