Thermodynamic State | Gibbs’ Phase Rule | Thermodynamic Equilibrium

By | February 7, 2019

Thermodynamic state

A system will be called in a particular thermodynamic state if it satisfies both the below mentioned criteria.

  1. All the thermodynamic properties of the system are uniform throughout the system
  2. All the thermodynamic properties of the system remain constant with respect to the time (at least for that moment)

Note: all the properties of the system are called state variables

But we all know there is a very large number of state variables

Here arises a question

If we have to fix all the properties of a system to define a thermodynamic state?

The answer is NO

We have to define only a minimum number of properties to define a system.

Those minimum number of properties are obtained from Gibbs phase rule.

Gibbs’ Phase rule:

F = C – Ø + 2


F = Number of independent intensive properties required to define the system

C = Number of components in the system

Ø = Number of phases of the system

For example:

For pure liquid water we have

C = 1

Ø = 1

Which gives

F = 2

Which implies that we need only two properties to define the state of water.

For more read two property rule for pure substances

If a thermodynamic state of a system remains invariable with respect to the time then we say that the system is in thermodynamic equilibrium.

These are ways of achieving thermodynamic equilibrium.

  1. When a system is isolated from its surrounding
  2. When both system and surrounding are in same thermodynamic state. In this case system is defined as dead system.

Note: if a system is in thermodynamic equilibrium then we can say that there is no thermodynamic process is happening within the system.

Also read:

Macroscopic view to study thermodynamics

Laws of thermodynamics

Different types of pressures

What is a Point function?

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