Concept of Thermodynamics - Zeroeth Law of Thermodynamics

For a system to be in thermodynamic equilibrium the following conditions must be full filled:-

i) Mechanical equilibrium

ii) Thermal equilibrium

iii) Chemical equilibrium

Mechanical equilibrium:

When there is no unbalanced force between system and its surroundings, the system is said to be in mechanical equilibrium.

Thermal equilibrium:

When the temperature in all parts of system is same as that of surroundings, the system is said to be in thermal equilibrium.

Chemical equilibrium:

If the chemical composition is same throughout the system and surroundings it is said to be in chemical equilibrium.

Zeroeth Law of Thermodynamics:

This law was first enunciated by RH Flower in 1831. According to this law when two systems ‘A’ and ‘B’ are in thermal equilibrium with another system ‘C’ then ‘A’ and ‘B’ will also be in thermal equilibrium.

What does First Law of Thermodynamics infer us?

• It is impossible to derive any work without expenditure of an equivalent amount of energy in some other forms. 

• Heat absorbed by the system should be taken positive. Heat rejected by the system should be taken negative. 

• For an ideal gas the total kinetic energy (KE) of all its molecules is called internal energy(U). For such a gas the internal energy depends only on Temperature.