Thermodynamics for JEE Chemistry

Thermodynamics is etymologically derived from the two base words of therm meaning heat and dynamics meaning movement. Thermodynamics deals with the processes involving:

  • the transfer of heat,
  • generation of heat,and
  • the transformation between different forms of energy which may sometimes occur in the form of heat generation.
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The initial application of thermodynamics was to the physical processes involving steam engines. It brought about higher conversions which were then extended to the chemical domain and used to analyse the reaction processes involved, and the feasibility of these reactions.


Scottish physicist Lord Kelvin was the first to formulate a concise

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definition of thermodynamics in 1854. This definition stated it as the subject of the relation of heat to forces acting between linked and interdependent parts of bodies, and the relationship of heat to the electrical agency.

Several chemical reactions and physical processes involve the generation of heat and transformation of various forms of energy. It is the study of these which form a part of the entire subject of thermodynamics for JEE chemistry.


Thermodynamics in Physics vs. Thermodynamics in Chemistry

Thermodynamics was born out of thermodynamics for physics, and it started as the study of heat, temperature, and their linkage to energy and work.

The thermodynamics in physics was primarily used to study concepts related to the designing and operation of heat engines. A heat engine is a system that converts heat, or thermal and chemical energy, into mechanical energy. The goal was to convert one form of energy into another kind of energy without significant losses. The lesser the losses, the better the system was, and the better was the operation of the heat engine.

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Thermodynamics in Physics gave rise to Chemical Thermodynamics (also termed Thermochemistry), which started with the principles of Thermochemistry similar to the principles of thermodynamics. Thermochemistry and chemical thermodynamics helped increase the vast knowledge we have in this domain of energy transfer.

Chemical Thermodynamics

Chemical thermodynamics deals with the heat involved in a combustion reaction. The use of entropy along with Gibbs free energy parameter as one of the measures to predict the feasibility of any reaction, internal energy, enthalpy, the heat of formation of substances, and many more. The thermodynamics for JEE chemistry can be broadly studied under three main energy exchange headings:

  1. Chemical Reactions –
  2. Different chemical reactions have different energy exchanges. The type of reaction such as exothermic and endothermic reactions also have effects.

  3. Phase Changes –
  4. The transition of a substance from one phase to another also involves the energy transfer and requirement.

  5. The Formation of the Solution –
  6. The formation of a solution of two substances always involves the formation of new bonds after rupturing of old bonds which exist for the individual elements. Hence, if the formation of the solution is practically feasible, the energy of the system decreases and the formed bonds are much more stable than the existing bonds in individual substances.

As per the revelations and discoveries, the Gibbs free energy should be decreasing, and the corresponding change in entropy should always be positive for the successful occurrence of any chemical reaction and interaction of two elements.

Laws Governing Thermodynamics

The science of thermodynamics is governed by four significant equations which are known as the zeroth law, the first law, the second law, and the third law. These laws have been framed after some of the most common and unquestionable observations. Hence they are some axiomatic rules.

The zeroth law is a statement of thermal equilibrium of bodies. It states that if two bodies are in thermal equilibrium with any third body, then they are in thermal equilibrium with each other as well.

The first law is derived from the concept of conservation of energy – “Energy can neither be created nor destroyed”. It brings a relation between the various forms of energy and brings into the three forms of energy namely the internal energy, the heat supplied to the system and work done by the surroundings on the system.

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The second law is related to the degree of randomness of an isolated system–which is termed the entropy of the system. As per the second law of thermodynamics, the entropy of an isolated system is always increasing. The consequences of the second law are the inability of transfer of heat from a cold body to a hot body and the melting of ice over time when exposed to an ambient environment. Both of these involve the increase in the randomness of the system. Any process which leads to an increase in the randomness or a decrease in the packing strength or lattice energy of the system is spontaneous.

The third law deals with the concept of absolute zero temperature. As per the various processes involved in the entire universe, it is very tough for matter to reach a temperature as low as absolute zero, i.e., OK. The states of matter cease to exist at such low temperatures. Since this temperature is so difficult to obtain, the entropy of a perfectly crystalline substance is zero at absolute temperature. As a consequence, this law states the non-attainment of the absolute temperature of 0K by any finite number of possible processes.

Important for JEE Thermodynamics

Thermodynamics is an essential part of the syllabus of JEE Chemistry. The fundamental concepts can be broadly categorized into four broad headings, namely:

  1. Internal Energy

  2. Enthalpy

  3. Entropy

  4. Gibbs Free Energy

You should have a sound grasp on each of the concepts above, and prepare everything which is a consequence of these four terms and the four laws of thermodynamics. You should try to visualize every concept as it is one of the most targeted areas, and contributes to one of the major sections in the paper.

Whatever the difficulty level of the paper is, you can find this section to be the one scoring. This includes every concept: the reaction enthalpy, the heat of formation, the Hess law of constant heat summation, Carnot engine, PV diagrams, work done for various systems, and the calculation of entropy of various systems.


Thermodynamics forms an integral part of the universe. You can quickly learn these concepts through the study of the prescribed syllabus and textbooks, or by physical observation.

Nothing here is superficial. Thermodynamics is a result of various observations made by people over the years, and is one of the subjects where there are so many axiomatic relations which have stood the test of time.

Conservation of energy is a vital thing that the world is currently focusing on. Getting to know the inter-conversion of one form of energy to another, its transmission, its movement, and the way it affects our lives, are some of the most vital and essential parts of the current human era. You should always try to relate the concepts to the world around you, which in turn should help you learn better.

There is still so much to improve in thermodynamics–such as developing an engine which is a hundred percent efficient and able to convert one form of energy into another without significant energy losses. Added to this is the need to minimize the amount of heat liberated in chemical reactions, the prediction of the reaction of various elements chemically, along with their bond strength and stability.

Moreover, thermodynamics finds its advanced forms in engineering streams, as well as mechanical and chemical engineering. Here there are more diverse topics to demonstrate what a significant role thermodynamics plays in the universe.

Thus, you should try to focus on the basic four terms and four laws to have a command over the entire concept of thermodynamics for JEE chemistry.

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