Basics of Thermodynamics

What is thermodynamics?

Thermodynamics is the branch of Physics that deals with heat, temperature, energy and work.

Branches of thermodynamics

Following are the branches of thermodynamics that are developed for various systems. These are:

  • Classical thermodynamics: Macroscopic interpretation of measurable properties which is used in the modeling of exchange of heat, energy and work.
  • Statistical thermodynamics: Microscopics interpretation ie; of atoms and molecular theories are studied. This is also known as statistical mechanics.
  • Chemical thermodynamics: Study of the interrelation of chemical reactions and energy.
  • Equilibrium thermodynamics: Study of matter and energy transfer from one thermodynamic equilibrium to another. For systems that don’t include equilibrium, non-equilibrium thermodynamics is used which is one of the branches of thermodynamics.

Laws of thermodynamics

There are four laws of thermodynamics and they are:

  • Zeroth law of thermodynamics: According to zeroth law, if two systems are in thermal equilibrium with the third, they are said to be in thermal equilibrium with each other also.
  • First law of thermodynamics: According to the first law, energy is exchanged between the systems as heat and work.
  • Second law of thermodynamics: According to the second law, for natural thermodynamics process the sum of entropies increases.
  • Third law of thermodynamics: According to third law, as the system reaches absolute zero, entropy reaches constant.

Types of systems

Thermodynamic systems are classified depending upon the boundaries through which mass, work and heat can flow. They are:


System type Mass Heat Work
Open system Yes Yes Yes
Closed system No Yes Yes
Thermally isolated No Yes No
Mechanically isolated No No Yes
Isolated system No No No


Types of processes

A thermodynamic process is defined as the study of thermodynamic proceedings from the initial state to the final state. Following are the commonly studied thermodynamic processes:

  • Adiabatic process: When there is no gain or loss of energy by heat
  • Isenthalpic process: At constant enthalpy
  • Isentropic process: At constant entropy
  • Isobaric process: At constant pressure
  • Isochoric process: At constant volume
  • Isothermal process: At constant temperature
  • Steady state process: When there is no change in the internal energy

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