In thermodynamics, define : (a) Mechanical equilibrium (b) Chemical equilibrium (c) Thermal equilibrium

Answer:

(a) Mechanical equilibrium: A system is in mechanical equilibrium when there are no unbalanced forces within it or between it and its surroundings, so the pressure is the same throughout the system and equal to that of the surroundings (no macroscopic motion).

(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 (for example by diffusion), so its chemical composition remains constant.

(c) Thermal equilibrium: A system is in thermal equilibrium with itself and its surroundings when its temperature is the same everywhere and equal to that of the surroundings, so there is no net flow of heat.

A system that is in all three equilibria is said to be in thermodynamic equilibrium.