Thermodynamics Equilibrium | Properties of Thermodynamic System | Pure Substance
Thermodynamic equilibrium
Thermodynamic state is a condition of a system and is specified by its thermodynamic properties. Thermodynamic Equilibrium of a system is a state such that if the system is isolated from its surroundings no change in thermodynamic properties would occur.
A system will be in a state of thermodynamic equilibrium if the conditions is satisfied for the following type of equilibrium.
i) Mechanical equilibrium
No change would occurs due to force within the system if it is isolated from the surroundings i.e., within the system all forces are balanced (absence of unbalanced forces)
ii) Thermal equilibrium
No temperature change occur within the system if it is isolated from its surroundings.
iii) chemical equilibrium
No change would occur in the chemical composition or no reaction would occur within the system if it is isolated from its surroundings. Two systems exist in chemical equilibrium if their chemical potential is same.
In general if a system is in equilibrium on its own will mean that it is in thermodynamic equilibrium.The two systems are said to be in equilibrium if no change occurs when They brought together and enclosed by a isolating boundary.
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Equilibrium
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Criteria
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Equality of temperature
Equality of force that is absence of unbalanced forces
Equality of chemical potential
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The above conditions must be satisfied for Thermodynamic Equilibrium.
Properties of a system
Any measurable characteristics of a system are called properties. Thermodynamic properties are independent of the shape of a particular system and does not require an external reference frame to define its value, e.g., mass, volume, pressure, temperature,etc
Properties may be classified as
1. Intensive properties and 2.Extensive properties
1.Intensive properties
Intensive properties are independent of the amount of substance present in a system pressure, temperature, and density etc., are intensive properties
2.Extensive properties
Extensive properties depend on the amount of substance present in a system mass, volume, energy etc., are extensive properties
An extensive property for unit mass such as a specific volume is an intensive property
Pure substance
Homogeneous substance with uniform chemical composition throughout its mass is called pure substance. A mixture of two or more phases with same chemical composition is called pure substance. For example a mixture of water (liquid phase) and ice (solid phase) is a pure substance. Air which is mixture of several gases is considered to be pure substance because it has a uniform chemical composition.
