Thermodynamics is a branch of science which deals with the heat ,work ,temperature and energy. The word “THERMODYNAMICS” comes from the greek words “theme”(heat) and “dynamikos”(energy).   In broad terms, thermodynamics deals with the transfer of energy from one to another place or to one form of energy to another form of energy.

    A heat engine is a good example of thermodynamics. It makes use of the properties of thermodynamics to transform heat into work. There are some  example of heat engines such as gasoline and diesel engines, jet engines, and steam turbines.

      Thermodynamics is based upon the observation of common experience which have been formulated into thermodynamics laws. These laws are based upon the principles of energy conversion.

   There are two points of view from which the behaviour of matter can be studied in thermodynamics: The Macroscopic and The microscopic.

  1. The Macroscopic approach- a certain quantity of matter is considered ,without the events occurring at the molecular level being taken into account.
  2. The Microscopic approach-matter is composed of myriads of molecules.


A thermodynamic system is defined as quantity of matter in space which attention is concentrated in the analysis a problem. Everything external to the system is called the surrounding or environment. The system is separated by boundary. Together the system and surrounding comprise a universe.

      There are three types of system.

  • Closed system- In a closed system mass is fixed. It means there is no exchange of mass. There may be energy transfer from one to another system.example-pressure cooker,a gas confined between a piston and cylinder.
  • open system- In an open system mass and energy both can transfer.most of the engineering devices are generally open system.example-an air compressor in which air enters at low pressure and leaves at high pressure and there is energy transfer across the boundary.
  • Isolated system- The isolated system is the one in which there is no interaction between mass and energy. Example-perfectly insulated closed and rigid vessel .

Control volume

   For an open system analysis such as air compressor ,attention is focused on a certain volume in space surrounding the compressor ,known as the control volume .matter as wel as the energy crosses the control surface.

  A closed system is a system to matter flow ,though its volume can change against a flexible boundary .when there is matter flow,then the system is considered to be a volume of fixed identity ,the control volume.  

  There is thus no difference between open and closed system.


    Thermodynamic properties- every system has its own characteristics by which its physical condition may be described example- volume, Temperature, volume. Such characteristics known as properties of system. Properties may be of two types:

  • Intensive properties- the properties which are independent of mass.example-pressure, temperature .
  • Extensive properties-the properties which are dependent of mass. Example- volume,energy.

Thermodynamic processes-the operation which brings change in state of the system.

Thermodynamic cycle –it consist of a linked sequence of thermodynamic processes that involve transfer to heat and work into and out of the system


A system is said to be in a state of equilibrium when no change in any macroscopic property is registered, if the system is isolated from its surroundings.

   A system will be in a state of thermodynamic equilibrium ,if the following three types of equilibrium are satisfied –

  • Mechanical equilibrium-a system is said to be in mechanical equilibrium if there is no unbalanced force exist.
  • Chemical equilibrium- a system is said to be in chemical equilibrium if there is no chemical reaction or transfer of matter from one part to another.
  • Thermal equilibrium- a system is said to be in thermal equilibrium if no spontaneous change in any property of the system.

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