A system is said to be exist in a state of thermodynamic euilibrium when no change in anymacroscopic property is registered, if the systrem is isolated from its surroundings. thermodynamic studies mainly the properties of physical systems that are found in equilibrium states. to be in thermodynamic EQUILIBRIUM IDEALLY SPEAKING SYSTEM SHOULD be isolated or in a dead state.

Dead state means, system properties = surrounding properties.

A system will be called in a state thermodynamic equilibrium if the conditions for the following three types of equilibrium are satisfied.

1. Thermal equilibrium:

The thermal equilibrium will be attained if both system and surrounding reach to the same temperature to stop further heat flow.

• Two systems at the same temp. No heat transfer Temp. gradient = 0

1. Mechanical equilibrium:

In absence of any unbalance force within the system itself or between system and surrounding the system is said is said to be in a state of mechanical equilibrium.

• equilibrium w.r.t. work transfer between system and surrounding. No imbalance of any properties that will cause work transfer. No imbalance of pressure of the system and surrounding pressure gradient=0

3. Chemical equilibrium: If there is no chemical reaction or transfer of matter from one part of the system to another such as diffusion, solution, the system is said to exist in a state of chemical equilibrium.

• equilibrium of the system w.r.t. chemical reaction and mass transfer. chemical composition does not change with time. concentration gradient=0,