Home » Thermal Engineering » What is Thermodynamics and 3 Laws of Thermodynamics

What is Thermodynamics and 3 Laws of Thermodynamics

What is Thermodynamics?

This article is about the laws of thermodynamics. Thermodynamics is a branch of the science of energy and it transmits the heat from one form another form.

It mainly deals with the heat and works energy and their effect on the properties of substances. The word thermodynamics comes from the Greek words, thermal means heat, and dynamics means power.

Though the study of thermodynamics started with the analysis of heat engine processes to improve engine efficiency. Today its scope is widened and there are important applications of the thermodynamics principles outside the field of heat engines.

Laws of Thermodynamics 

There are three laws of thermodynamics:

  • Zeroth law of thermodynamics
  • First law of thermodynamics
  • Second law of thermodynamics

Zeroth law of Thermodynamics 

It states that

”when two bodies are in equilibrium with a third body, then they are also in thermal equilibrium with each other.

Zeroth law of thermodynamics

For example, if bodies AB in thermal equilibrium with body C, then A & B must be in thermal equilibrium with each other.

First Law of Thermodynamics

  • It states that ”the heat and work are mutually convertible”. it is the law of conservation of energy.
  • i.e, energy can neither be created nor destroyed, but it can convert into another form of energy.
  • If a thermodynamic system is operating in a closed cycle, then the heat transfer is directly proportional to the work transfer.
  • Mathematically according to this law, we have
First law of thermodynamics


  • Q = Heat supplied
  • W = external work done
  • du = change in internal energy

Second Law of Thermodynamics

This law states.

” There is a definite limit to the amount of mechanical energy, which can be obtained from a given quantity of heat energy.”

It is explained by using two different statements,

Second law of thermodynamics

Clausius statement – This law of thermodynamics has been enunciated by Clausius in a slightly different form, as

“it is impossible for a self-acting machine working in a cyclic process, to transfer heat from a body at low temperature to a body at a high temperature without the external use or heat cannot flow from a cold body without use”.

Or in other words, the heat cannot flow itself from a cold body to a hot body without the help of an external agency.

Kelvin-Planck statement – It states that

“It is impossible to construct an engine working on a cyclic process, whose purpose is to convert all heat energy into work”.

In other words, no actual heat engine, working on a cycle process, can convert the heat energy supplied to it into mechanical work. It means that there is a degradation of energy in the process of producing mechanical work from heat. According to this statement, the second law of thermodynamics is sometimes called the law of degradation of energy.

That’s it Thanks for reading. Have any question leave a comment I’ll respond.

Read more on this blog:

  1. Shaper machine and types of shaper machine
  2. Types of micrometre screw gauge
  3. Reciprocating pump and working principle.
About Saif M

Saif M. is a Mechanical Engineer by profession. He completed his engineering studies in 2014 and is currently working in a large firm as Mechanical Engineer. He is also an author and editor at www.theengineerspost.com

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.