Thermodynamics: the study of Work, Heat & Energy


What is Thermodynamics?

The branch which deals with the the movement of energy from one form to the other and the relation between heat and temperature with energy and work done is called as thermodynamics. In other terms we can define thermodynamics as the science stream that deals with the study of the combined effects of heat and work on the changes of state of matter confined by the laws of thermodynamics. Chemical reactions which releases heat energy associated with it are converted into different usable forms based on the laws of thermodynamics. The fact that energy can only be transformed from one form to the other forms and its use in different industries is on the basis of energy transformation. We are aware that chemical reactions have energy associated with it. The laws of thermodynamics deal with energy changes during a reaction and are not concerned with the rate at which the reaction is proceeding.

Define Chemical Thermodynamics

Chemical thermodynamics is the study of relation between work, heat and chemical reactions or with the physical changes of the state which are confined to the laws of thermodynamics.

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 referred to the energy content within the system. The energy represents the overall energy of the system and may include many forms of energy such as potential energy, kinetic energy etc. In a chemical reaction, we know about the energy transformations and basic thermodynamics provides us with the information regarding energy change associated with the particles of the system.

Factors affecting the internal energy

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.


Work done by a system is defined as the quantity of energy exchanged between a system and its surroundings. Work is completely governed by external factors such as an external force, pressure or volume or change in temperature etc.


Heat in thermodynamics is defined as the kinetic energy of the molecules of the substance. Heat and the thermodynamics together form the basics which 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.


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. The surrounding and universe interact with each other and depending on the type of the system, exchange of matter and energies occur. The system’s classification entirely depends 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 energy, as well as matter takes place, are treated as an open system. For example, water is boiled on a stove without it being covered, the container behaves as an open system because it receives heat energy from an external source and the matter being released are water vapours.

  1. Closed System:

A closed system is referred to the system where only energy can be exchanged with the surrounding and not the matter. It can also be said that a closed system has a constant amount of matter and only the energy of the system can be changed. For instance, when we keep a shield bottle of water in the fridge, the loss of energy to the surrounding will result in the temperature of the water inside it going down even though the quantity of water in the bottle remains the same.

  1. Isolated System:

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

Let us see the major aspects on which environment can affect the thermodynamics of a system.

State Functions Affecting Thermodynamics:

There are four laws which govern the thermodynamic systems’ phenomena, they are:

Laws of thermodynamics:

  • First law of thermodynamics: When energy moves into or out of a system, the system’s internal energy changes in accordance with the law of conservation of mass.
  • Second law of thermodynamics: The state of the entropy of the entire universe, as an isolated system, will always increase over time.
  • Third law of thermodynamics: Entropy of a perfect crystal at absolute zero is zero.

The laws of thermodynamics was the most important lesson for people understanding the mechanism behind phase change of matter.

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

Practise This Question

In thermodynamics which one of the following is not an intensive property