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Question1: Explain briefly the following terms in thermodynamics.

  • System
  • Surrounding
  • Boundary
  • State Variables



The quantity of matter or region of space whose behavior is being studied is called system.

For example some quantity of gas enclosed in a cylinder is considered to be a system. We can study the behavior of the enclosed gas by thermodynamic variables pressure, volume, temperature etc.


Everything other than the system in the universe is called surrounding of the system.


The region which separates the system from the surrounding is called boundary.

Thermodynamically, any exchange of energy between the system and surrounding takes place through the boundary. For example, such exchange can be carried out through work done by or on the system or by inor out flow of the heat.

State Variables

The variables or functions which determine the physical state of the system are called variable or state functions.

If the system is homogeneous, i-e, it has the same composition in all parts of it, then pressure P, volume V and temperature T are sufficient parameters to know about the thermodynamic state of the system.These parameters are related by

PV = nRT
(n = number of moles)

However, this equation is applicable to ideal gas only. The exact relation of these parameters is not known for solids, liquids or non-homogeneous substances.


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