Equilibrium

Definition

Equilibrium is the state of a thermodynamic system where all macroscopic flows are balanced and properties do not change over time. In this state, the system’s temperature, pressure, and chemical potential are uniform throughout.

5 Must Know Facts For Your Next Test

1. In thermal equilibrium, two systems in contact will exchange no net heat energy.
2. Mechanical equilibrium occurs when there are no unbalanced forces within the system.
3. Chemical equilibrium is achieved when the chemical potentials of all substances in a system remain constant over time.
4. Equilibrium can be dynamic, involving continuous microscopic changes while maintaining macroscopic constancy.
5. The concept of equilibrium is essential in applying the First Law of Thermodynamics to closed systems.

Review Questions

• What conditions must be met for a thermodynamic system to be in equilibrium?
• Describe what happens to heat transfer between two systems in thermal equilibrium.
• How does mechanical equilibrium differ from thermal or chemical equilibrium?

Related terms

First Law of Thermodynamics: $\text{Energy cannot be created or destroyed, only transferred or transformed.}$ Also known as the conservation of energy principle.

Thermal Equilibrium: $\text{A specific type of equilibrium where two objects connected by a permeable barrier have equal temperatures.}$

Chemical Potential: $\text{The change in free energy when particles are added to a system at constant temperature and pressure.}$