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equilibrium

ee-kwih-LIB-ree-uhm /ˌiːkwɪˈlɪbriəm/

nounC1GREGMATCATUPSC

academictechnical

A state of physical balance in which opposing forces, influences, or processes are equal and stable.

In thermodynamics, 'thermal equilibrium' specifically means that two connected systems have reached the exact same temperature, resulting in zero net heat transfer between them.

The story behind the word. Equilibrium is born from two Latin words: 'aequus', meaning 'equal', and 'libra', meaning 'a balance or pair of scales'. It represents the perfect balancing of a scale where neither side outweighs the other.

Word relationships

balance: Balance is a general term for equal distribution of weight or forces, while equilibrium is a formal scientific term for stable physical or chemical states.

imbalance: Imbalance refers to an unequal distribution of forces or quantities, preventing a stable state.

Commonly confused with

stability: Stability is the ability of a system to return to its original state after a disturbance, whereas equilibrium is the state of balance itself.

Word family

equilibrate (verb): To bring into or keep in equilibrium.
equilibration (noun): The act of restoring or achieving balance.

Collocations

thermal equilibrium
reach equilibrium
state of equilibrium
dynamic equilibrium

Example sentences

"When a hot stone is dropped into cold water, they will eventually reach thermal equilibrium." Thermodynamics principle
"The chemical reaction reached equilibrium when the rate of the forward reaction equaled the rate of the reverse reaction." Scientific paper on chemical systems

Memory hook

Think of 'equal' and 'libra' (the astrological sign of the scales). When the scales are equal, you have reached equilibrium. Perfect balance on the scales.

When not to use

Do not use to describe a system that is actively changing, fluctuating, or experiencing unbalanced forces.

Fun facts

The 'Zeroth Law of Thermodynamics' is entirely about equilibrium: if system A is in equilibrium with system B, and B is in equilibrium with C, then A is in equilibrium with C. This simple law is what makes thermometers possible!