Equilibrium in any physical process has the following characteristics :
i Equilibrium is established only in a cloud system at a certain temperature.
ii At equilibrium both the opposite reactions occur at the same rate. These have a dynamic but permanent state.
iii All measurable properties of the system are constant. When equilibrium is established in any physical process, then stability of melting point, vapour pressure etc., identify equilibrium.
iv The value of various quantities at any time shows to what extent the process has progressed before reaching equilibrium.