In a thermodynamic system, define – (a) Mechanical equilibrium (b) Chemical equilibrium and (c) Thermal 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. The pressure is then the same throughout the system and equal to that of the surroundings, and there is no macroscopic movement.

(b) Chemical equilibrium: A system is in chemical equilibrium when there are no net chemical reactions within it and no net transfer of matter (for example by diffusion) from one part to another, so its chemical composition remains constant with time.

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

A system satisfying all three is in thermodynamic equilibrium, and its state variables (P, V, T) have fixed values.