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Chemistry > Thermodynamics > Thermodynamic Terms

Thermodynamic Terms

Has your teacher explained the concept of thermodynamics to you? You must have heard of the terms like energy, work and heat etc. Let us tell you, these are all thermodynamic terms. In this topic, we will look at the thermodynamic terms and understand what are these. However, we will start our lessons from the basic concept of thermodynamics. Only then can you understand its applications easily.

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What is Thermodynamics?

Thermodynamics is the branch of science primarily dealing with the study of the combined effects of heat and work with changes in state. These changes and effects follow certain laws, the laws of thermodynamics.

The heat energy released or absorbed in different chemical reactions converts into different usable forms following the laws of thermodynamics. We know that we can neither create energy nor destroy it. In fact, we can only convert it from one form to another. This principle is the basis of energy transformation and its use in different industries is a major application of thermodynamic terms.

Chemical reactions also have varying amounts of energy linked with themselves. Thermodynamics is nothing but the study of the flow of energy from one form to another. It also studies the relation between heat and temperature with energy and work done.

The laws of thermodynamics concern themselves with energy changes during a reaction. They are not related to the rate at which the reaction is proceeding. We often use some general terms like work, heat and energy in thermodynamic terms. Let us now learn quite a bit about these terms and understand them properly.

Browse more Topics under Thermodynamics

Internal Energy

It is the energy that a system stores within itself. This energy stands for the total energy of the system. It could include any form of energy: kinetic energy or potential energy, etc. We know about the energy transformations. We are aware that we can transfer energy and not create or destroy it.

Basic thermodynamic terms gives us an idea regarding the energy change associated with a system of chemical reaction. Whenever heat passes into or out of a system, the internal energy of any system could alter. We can say that work is done on the system or by the system. We can also put in as: matter enters or leaves the system.


According to thermodynamics, work done by a system is the total quantity of energy that the system and its surroundings exchange within themselves. The external factors in the surroundings govern the amount of work done. These factors could be an external force, changes in the temperature or pressure or volume, etc.


Thermodynamics define heat as the energy in transit. It is the energy that kinetic energy of the molecules of the substance possessed. Heat and the thermodynamics play an important role in helping process designers and engineers optimize their processes.

It also helps them to harness the energy associated with chemical reactions economically. Heat flows from higher temperature to lower temperature. This particular concept helps scientists to design various heat engines.

Thermodynamic System and the Surrounding

Thermodynamic Terms

After all, this discussion, doesn’t the question “What is a system” bother you? A system is the part of the universe under study. It refers to the part where we make the observations. The rest of the universe constitute the surrounding. We can divide the system into two main types, based on the nature of the movement of energy and matter in or out of the system. They are:

Open System

These are the systems where the exchange of matter, as well as energy, both take place. An example of this would be the case when we boil water on a stove. The container acts as an open system as it receives heat energy from outside and the matter comes out as water vapours.

Closed System

Closed systems refer to those where only energy is exchanged with the surrounding and not the matter. When we keep a closed bottle of water in the fridge, the quantity of water in the bottle remains the same. However, it loses energy to the surrounding as a result of which the temperature of the water inside it goes down.

There is another type of system, the isolated system. Here, neither energy nor matter can be exchanged between the system and the surrounding. An example of such a system would be thermos flask.

Solved Examples for You

Question: State the laws of thermodynamics.

Answer: The laws of thermodynamics govern the way energy is transferred from one state to another. They are:

  • First law of thermodynamics: When energy moves into or out of a system, the systems 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 application of these laws in various industries has led to a number of significant inventions and discoveries for the good of the mankind. Whether it is a refrigerator or a cooker, you can see the magic of thermodynamics.

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