Thermodynamics

All forms of energy are inherently interrelated. The movement of microscopic particles in an object produces heat and determines its intensity. The energy radiated by that heat is known as thermal energy. 

Under certain conditions, energy can also be transformed into one form from the other. Similarly, thermal energy can also be transformed into another form of energy. And thermodynamics is basically the study of such energy transformations.  

What is Thermodynamics?

Thermodynamics is the science of the relationship between heat, work, temperature and energy. It tries to explain how thermal energy is converted to or from other forms of energy and what effects it has on matter.

For example, when you burn fuels like methane and coal, the chemical reaction that occurs releases the chemical energy stored in the molecules in the form of heat. This chemical energy transformation can be used for mechanical works and to produce electrical energy. 

Being a field of macroscopic science, thermodynamics does not concern with how and at what intensity these energy transformations occur. It only concentrates on the initial state and the final state of the change. It deals with the bulk system of a matter rather than its molecular constitution. 

The Discovery of Thermodynamics

While the laws of thermodynamics are omnipresent and ever-existent, the field of studying thermal energy dates as far back as 1798 when Sir Benjamin Thompson proved heat to be a form of energy. It paved a path to a whole new domain of physics that concentrated on transforming thermal energy into another form of energy. 

Another notable pioneer of thermodynamics was a French military engineer named Sadi Carnot, who introduced the world to the concept of the heat-engine cycle and the limits of the steam engine. He is also known as the ‘father of thermodynamics’ who coined the second law of thermodynamics. 

While thermodynamics was initiated as a study to understand the potential of steam engines and thermal energy, it has become a vital instrument to understand the complete description of all types of changes in the energy state of any system. 

Laws of Thermodynamics 

While we discussed that thermodynamics does not concern how the state of energy changes, there are a certain set of laws that govern the transformation. The laws of thermodynamics help you understand how fundamental physical quantities like temperature, energy, and entropy will behave under various circumstances. 

There are four laws of thermodynamics: 

Zeroth Law of Thermodynamics 

According to the zeroth law of thermodynamics states that: ‘If two bodies are individually at the state of equilibrium with a separate third body, then you can say that the first two bodies are also in thermal equilibrium with each other.’

So, if object A is in thermal equilibrium with object B and object C is also in thermal equilibrium with object B, then you can say that objects A and B are in thermal equilibrium with each other. This law gave the concept of temperature.

First Law of Thermodynamics 

Also known as the law of conservation of energy, the first law states that: ‘Energy can neither be created nor destroyed. However, it can be transformed into one form from the other.’

According to this law, when heat is transferred from one system to another, the total energy transferred is dispersed between changing the internal energy of the system, and the rest is used by the system to conduct that process. 

This law can be explained with this equation:

ΔQ = ΔU + W

Where, 

ΔQ refers to the heat given or lost 

ΔU refers to change in the internal energy 

W refers to the work done

Second Law of Thermodynamics 

The second law of thermodynamics states that: ‘the entropy in an isolated system will always increase. Any isolated system aims to reach the state of maximum entropy of the system.’’

Entropy is a thermodynamic function that is used to measure the disorder or randomness of a system. It is calculated in terms of a thermodynamic quantity whose value is dependent on the physical state and condition of a system. For example, in a solid where the particles are not free to move, the entropy will be less than that of a gas, where the particles can roam freely in a container. 

So, according to the second law, the entropy of the universe will always keep on increasing and never decrease. 

Third Law of Thermodynamics 

The third law of thermodynamics states that: ‘The entropy of a system approaches a constant value when the temperature reaches absolute zero.’

Let’s take water as an example. When you reduce the temperature of boiling water from 100℃, the steam gets converted from gas to water, where the particles are restricted, and the entropy level is decreased. Further, if you cool the water to 0℃, it becomes solid where the movement is further restricted, and the entropy decreases further. 

Conclusion  

Energy is an ever-constant element that can neither be created nor destroyed and pertains throughout the universe. The state of energy is only governed by the laws of thermodynamics, which helps us understand how fundamental physical quantities like temperature, energy, and entropy will behave under various circumstances.