Thermodynamics: the study of Work, Heat & Energy


What is Thermodynamics?

Thermodynamics is the sub-division of science that deals with the study of the combined effects of heat and work with changes in state confined by the laws of thermodynamics. Heat energy associated with chemical reactions is converted into different usable forms based on the laws of thermodynamics. The fact that energy can never be created nor destroyed and can only be transformed from one form to the other forms on the basis of energy transformation and its use in different industries is an application of thermodynamics. Chemical reactions also have energy associated with them. The study of the flow of energy from one form to the other and the relation between heat and temperature with energy and work done is called as thermodynamics. The laws of thermodynamics deal with energy changes during a reaction and are not concerned with the rate at which the reaction is proceeding.

Some general terms like heat, energy, and work were done are often used in thermodynamics. Let us learn a bit about basic thermodynamics and understand these terms.

Internal Energy:

It is the energy stored within the system. This energy represents the total energy of the system and may include any form of energy, kinetic energy, potential energy, etc. We know about the energy transformations, energy can only be transferred and cannot be created or destroyed. Basic thermodynamics provides us with the information regarding energy change associated with a system of chemical reaction. The internal energy of a system may change when heat passes into or out of the system, work is done on or by the system or matter enters or leaves the system.


Basic thermodynamics defines work done by a system as the quantity of energy exchanged between a system and its surroundings. Work in thermodynamics is completely governed by external factors in the surroundings. These factors may be an external force, a change in temperature or pressure or volume, etc.


Heat in thermodynamics is defined as the energy in transit. It is the energy by kinetic energy of the molecules of the substance. Heat and the thermodynamics together form a vertical of science that has helped process designers and engineers to optimize their processes and harness the energy associated with chemical reactions economically. Heat energy flows from higher temperature to lower temperature. The study of this flow and advancements in thermodynamics has helped scientists to design various heat engines.


Experiment exploring the second principle of thermodynamics

Thermodynamic system and the surrounding: 

Thermodynamics defines a system as the part of the universe under study that is the part where observations are made. Any part of the universe other than the system constitutes the surrounding. The imaginary line that separates a system from the surrounding is called as the boundary line. The surrounding and universe interact with each other and exchange matter and energies depending on the type of the system. The classification of the system is solely based on the movement of energy and matter in or out of the system. There are two types of system:

  1. Open System:

    Those systems where the exchange of matter, as well as energy both takes place, are referred to as an open system. For example, when we boil water on a stove, the container is an open system as it receives heat energy from outside and the matter comes out as water vapours.

  2. Closed System:

    Those systems where only energy can be exchanged with the surrounding and not the matter are called as closed systems. In other words, we can say that a closed system has a constant amount of matter and only energy of the system can be changed. For instance, when we keep a shield bottle of water in the fridge, the quantity of water in the bottle remains the same but it loses energy to the surrounding as a result of which the temperature of the water inside it goes down.

  3. Isolated System:

    In case of isolated systems, neither energy nor matter can be exchanged between the system and the surrounding. Thermos flask is an example of an isolated system.

With thermodynamics having its roots in multiple subjects, let us see the major aspects on which chemistry has an effect on the thermodynamics of a system.

State Functions Affecting Thermodynamics:

There are four laws which govern how thermodynamic systems behave to certain thermodynamic phenomena. Let us list the laws of thermodynamics:

Laws of thermodynamics:

The laws of thermodynamics are one of the most important laws in the field of science and there is always more to learn. Their application in different industries has done wonders for humankind, whether it is a refrigerator or a pressure cooker, thermodynamics is everywhere.

To know how heat transfer works, how thermodynamics works and practice solving NCERT solutions for Thermodynamics with Byju’s.

Practise This Question

A system is any specified portion of matter which is separated from the rest of the universe with a definite boundary. T/F