For a thermodynamic system :Define : (a) Mechanical equilibrium(b) Chemical equilibrium

Answer:

(a) Mechanical equilibrium: A system is in mechanical equilibrium when there are no unbalanced forces within the system or between the system and its surroundings, i.e. the pressure is the same at all points of the system and equals that of the surroundings (if the wall is movable). Hence there is no change in volume.

(b) Chemical equilibrium: A system is in chemical equilibrium when there is no net chemical reaction and no net transfer of matter from one part of the system to another (e.g. by diffusion), so the chemical composition stays the same everywhere and does not change with time.