Thermodynamics in Physics and Chemistry: Definition, Laws & Difference

Heat is one of the essential entities for mankind. Without heat, life on earth or anywhere in the universe would be impossible. Thermodynamics deals with heat flow and other related concepts.

In this article, we will be learning about the concept of thermodynamics in a detailed manner while understanding how it is different in physics and chemistry.

Table of contents

Overview

Thermodynamics – Definition

Branches of thermodynamics

Concepts of thermodynamics

Thermodynamic process

Thermodynamic Systems

Thermodynamic properties

Laws of thermodynamics

Entropy

Enthalpy

The major difference between thermodynamics in physics and thermodynamics is chemistry

Thermodynamics in everyday life

FAQs

Thermodynamics – Definition

Thermodynamics is a branch of physics that deals with temperature, heat, and work related to radiation, energy, and other physical properties.

In simple terms, thermodynamics in JEE Main Physics demonstrates thermal energy conversion into other forms of energy. Additionally, it also explains how matter could be affected by this process. Heat is the main source of thermal energy. Heat can be seen produced due to the moment of small particles within an object. When the movement of these tiny particles is faster, more heat is being generated.

The main goal of thermodynamics is not about how these energy transformations are carried out. It is not about at what rates either. This process is completely based on the changes undergone by initial and final states.

Thermodynamics in JEE Main agrees with systems that have bulk entities. Therefore, it is not concerned about the matter’s molecular constitution. So, thermodynamics can be referred to as macroscopic science.

Branches of thermodynamics

Thermodynamics is ideally classified into four different branches. They are:

Chemical Thermodynamics
Statistical Thermodynamics
Classical Thermodynamics
Equilibrium Thermodynamics

Chemical Thermodynamics

It is the relation between work and heat in a chemical reaction. It also deals with changes of states.

Statistical Thermodynamics

All the molecules present in the thermodynamic systems are being considered in statistical thermodynamics. In simple words, this type of thermodynamics illustrates the properties of every molecule that is involved in the system as well as how they interact with one another is also being taken into account. This is done to classify the behaviour of molecules.

Classical Thermodynamics

This type of thermodynamics involves a macroscopic approach to examine the behaviour of matter. Here, units of pressure and temperature are being considered. This helps calculate and predict various other properties of matter that have undergone the process.

Equilibrium Thermodynamics

It is nothing but the understanding of energy and matter transformations as they approach the state of equilibrium.

Concepts of thermodynamics

Thermodynamics involves various amounts of concepts in it. The following are some of the most common thermodynamic concepts:

Thermodynamic process

Whenever there is an energetic change within the system, it indicates that it is undergoing a thermodynamic process. This process can be incorporated with internal energy, volume, and pressure changes.

The thermodynamic process involves four different processes, and all these processes have their unique features. The following are the types of thermodynamic processes:

Isothermal process:

In the isothermal process, there is no occurrence of temperature change.

Adiabatic process:

In this process, the heat transfer into and out of the system will be zero.

Isobaric process:

Here, there will be no pressure change involved.

Isochoric process:

There will be no work done here, as there is no volume change.

A thermodynamic system can be regarded as a cycle of processes, which are being conducted to equate the initial and final states of operation. This involves a combination of processes and can be called cyclic processes or cyclic operations.

Thermodynamic Systems

A thermodynamic system can be defined as a specific portion of matter containing a definite boundary that may be real or imaginary. Below mentioned are the three kinds of systems:

Open system:

Both energy and mass are transferable between the system and surroundings in this system. An example of an open system would be a steam turbine.

Closed system:

In a closed system, only the transfer of energy is possible across the boundary, whereas there will be no mass transfer. Examples of a closed system are gas compression in piston-cylinder arrangement, refrigerators, etc.

Isolated system:

An isolated system can’t exchange both mass and energy with its surroundings. An example of an isolated system is the universe.

The below-mentioned table gives a simple knowledge about the interactions of thermodynamic systems:

Type of system	Heat	Work	Mass flow
Open system	Yes	Yes	Yes
Closed system	No	Yes	Yes
Isolated system	No	No	No

Surrounding is a term used along with the system, which indicates the actions outside the system. Surrounding has a direct influence on each of the system’s behaviour.

Thermodynamic properties

These properties are capable of determining the characteristic features of a thermodynamic system. It also helps in identifying the state of the system. These properties can be either intensive or extensive.

Intensive properties:

These are the types of properties that do not completely rely on the matter’s quantity. Examples of intensive properties are pressure and temperature.

Extensive properties:

The value of extensive properties relies on the system’s mass. Some examples of this property are volume and energy, etc.

Laws of thermodynamics

Laws in thermodynamics are used to determine some of the essential physical quantities such as temperature, energy, entropy, etc. These are very much helpful in demonstrating thermodynamic systems at equilibrium. With the assistance of these laws, we can understand how behavioural quantities perform under various circumstances.

Thermodynamics contains four laws, they are:

Zeroth law of thermodynamics

This law indicates that if two different bodies are in equilibrium individually with another separate body, then the first two bodies are also in equilibrium with one another.

To illustrate, if system one is considered in equilibrium with three, system two is also in thermal equilibrium with the 3rd one. It automatically indicates that both the systems 1 and 2 are also in thermal equilibrium.

The first law of thermodynamics

The first law deals with an energy conservation law, which indicates that energy can neither be created nor destroyed. However, it could be possible to change from one state to another.

Given below is a very good example for the first law of thermodynamics:

Plants convert light energy into chemical energy using a process called photosynthesis. Humans consume plants, transforming chemical energy into useful work such as walking, running, doing multiple tasks, etc.

The second law of thermodynamics

This law illustrates that there will always be an increase in entropy in an isolated system. This system can evolve towards the equilibrium condition spontaneously. Therefore, there will only be an increase in the universe’s entropy, which will never reduce.

For instance, when we take a room that has not been cleaned for months, it will only become messy and dusty every day. It will never go back to its original state (cleaned) unless someone cleans it. Once it is cleaned, the entropy of the room decreases drastically. However, the efforts to clean it have increased the entropy outside of the room. This would exceed the entropy lost.

Third law of thermodynamics

When the temperature of a system reaches absolute zero, the entropy approaches a constant value. This is what happens in the third law of thermodynamics.

For example, the entropy is zero for a pure crystalline component whose temperature is absolute zero.

Entropy

Entropy is nothing but a quantity in thermodynamics, in which its value is fully dependent on the condition of a system. In simple words, entropy is the measure of the disorder or randomness of a system.

For instance, a solid’s entropy is lesser compared to the entropy of the gas. This is because the particles contained in solid are not free to move, whereas, in gas, the particles are allowed to move easily.

Enthalpy

Enthalpy is defined as the measurement of the energy contained in a system. Enthalpy’s quantity is equivalent to the system’s total heat content, which equals the system’s internal energy added to the product of pressure and volume.

Given below is the mathematical form for the same:

H = E + PV

Where,

H is the enthalpy,

E is the internal energy,

P is the pressure and

V is the volume.

The major difference between thermodynamics in physics and thermodynamics is chemistry.

Firstly, thermodynamics in chemistry and physics are fundamentally the same. Yet, there is one difference: nothing but the notation of work. This is given by:

In physics, the total amount of work done by the system can be seen as positive.
In chemistry, the total amount of work done on the system could be positive.

The main reason for this difference is that in physics, we are mostly just looking at the study of the system and what things this system can provide us. On the other hand, in chemistry, we are mainly focused on things that need to be done on the system to make some changes.

Thermodynamics in everyday life

From travelling by car to simply sitting in a room with an AC, thermodynamics is the most essential for everything. Listed below are some of the common applications of thermodynamics in our day-to-day lives:

Refrigerators involve a thermodynamic process to preserve food and keep it at low temperatures.
Vehicles such as cars, bikes, trucks, even planes use thermodynamics. They even run on the second law of thermodynamics.
The concept of heat transfers is vastly used in coolers, heaters, radiators, etc.

Frequently Asked Questions on Thermodynamics

How can thermodynamics be practised?

To physically practise thermodynamics, we should relate it to our everyday life. For example, if we want to make coffee, we should know how hot our milk should be and what the precipitation ratio of sugar and coffee beans would be etc. Likewise, we can do many household chores to understand it physically.

Define the Carnot cycle in thermodynamics.

The Carnot cycle can be demonstrated as an ideal closed cycle that is reversible. Here, the working component enters to perform four operations. Those are: