Equilibrium – Notes

Physical processes: Equilibrium
Equilibrium is a condition in which two opposing tendencies balance one another.
The opposing tendencies of a reversible change continue to take place with equal rates simultaneously at the equilibrium stage also. Hence, the equilibrium is called dynamic equilibrium.
Equilibrium can be established for physical as well as chemical processes.
At the equilibrium state, if there is a change in the physical state, the equilibrium is called physical equilibrium.
For any pure substance at atmospheric pressure, the temperature at which the solid and liquid are at equilibrium is called the normal melting point or normal freezing point of the substance.
The pressure exerted by the vapour over a liquid when it is in equilibrium with liquid at a given temperature, is termed as vapour pressure of the liquid at that temperature.
For any pure and liquid at one atmospheric pressure the temperature at which the liquid and vapours are at equilibrium is called the normal boiling point of the liquid.
The process of direct phase change from solid to vapour state without the intermediate liquid state is called sublimation.