Thermodynamic Equilibrium

Thermodynamic Equilibrium

• The two systems are said to be in thermodynamic equilibrium with each other
• When they are in mechanical, chemical and thermal equilibrium with each other.
• Here are various types of equilibrium and the conditions for thermodynamic equilibrium of the system.

• Let us suppose that there are two bodies at different temperatures, one hot and one cold. 
• When these two bodies are brought in physical contact with each other, temperature of both the bodies will change.
•  The hot body will tend to become colder while the cold body will tend to become hotter.
•  Eventually both the bodies will achieve the same temperatures and they are said to be in thermodynamic equilibrium with each other.
•  In an isolated system when there is no change in the macroscopic property of the system like entropy, internal energy etc, it is said to be in thermodynamic equilibrium. 
• The state of the system which is in thermodynamic equilibrium is determined by intensive properties such as temperature, pressure, volume etc.
• Whenever the system is in thermodynamic equilibrium, it tends to remain in this state infinitely and will not change spontaneously. 
• Thus when the system is in thermodynamic equilibrium there won’t be any spontaneous change in its macroscopic properties.

Conditions for Thermodynamic Equilibrium

• The system is said to be in thermodynamic equilibrium if the conditions for following three equilibrium is satisfied:

1) Mechanical equilibrium

2) Chemical equilibrium

3) Thermal equilibrium

1) Mechanical equilibrium: 

• When there are no unbalanced forces within the system and between the system and the surrounding, the system is said to be under mechanical equilibrium. 
• The system is also said to be in mechanical equilibrium when the pressure throughout the system and between the system and surrounding is same.
• Whenever some unbalance forces exist within the system, they will get neutralized to attain the condition of equilibrium. 
• Two systems are said to be in mechanical equilibrium with each other when their pressures are same.

2)Chemical equilibrium: 

• The system is said to be in chemical equilibrium when there are no chemical reactions going on within the system or there is no transfer of matter from one part of the system to other due to diffusion. 
• Two systems are said to be in chemical equilibrium with each other when their chemical potentials are same.

3) Thermal equilibrium: 

• When the system is in mechanical and chemical equilibrium and there is no spontaneous change in any of its properties, the system is said to be in thermal equilibrium. 
• When the temperature of the system is uniform and not changing throughout the system and also in the surroundings, the system is said to be thermal equilibrium. Two systems are said to be thermal equilibrium with each other if their temperatures are same.

Equilibrium

Equilibrium conditions

• The state of a body or physical system that is at rest or inconstant and unchanging conditions.
• Means equilibrium is a state of balance.
• To understand equilibrium let a simple example of a see-saw.
• If two persons having almost equal weight, sit on opposite sides of the see-saw and their distances from center point are same , then the see-saw would not be tilted.

• It is define as equilibrium condition of mass.

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Application of Equilibrium conditions in various engineering fields.

• Equilibrium implies the object is at rest (static) or its center of mass moves with a constant velocity (dynamic).
• Static equilibrium is a common situation in engineering.„
• Principles involved are of particular interest to civil engineers, architects, and mechanical engineers.
• In chemistry by the help of equilibrium we can study the phase diagrams and analyse boiling points, melting points, freezing points, triple pressure and temperatures of any component.
• For water the phase diagrams are shown
• 2 D phase diagrams

3 D phase diagrams

Reference more detail visit HTTP://Wikipedia/wiki/Phase_diagram

• In chemistry it also useful to study the reversible and irreversible reactions.
• The condition existing when a chemical reaction and its reverse reaction proceed at equal parts.