Physical Equilibrium
An equilibrium between two physical states or phases of the same substance.
Formula / equation
H₂O(l) ⇌ H₂O(g)
Unit
Dimensionless
In depth
No chemical bonds are made or broken; only the arrangement or state of the particles changes. Physical equilibria obey the same rules as chemical ones, so they respond to temperature and pressure changes according to Le Chatelier's principle, which is why boiling point varies with altitude.
Examples in the real world
A saturated salt solution in contact with undissolved crystals; ice and water coexisting at 0 °C.