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Laws of Thermodynamics | Zeroth, First, Second, and Third Law


In this article, we will discuss the four laws of thermodynamics

  • Zeroth law
  • First law 
  • Second law 
  • Third law

Let’s start by understanding the Zeroth law of thermodynamics.

Zeroth law states that if two systems are in thermal equilibrium separately from a third system, they must be in thermal equilibrium with each other. 

In other words, if two bodies are in thermal equilibrium, and a third body is placed in contact with them, then the temperatures of all three bodies will become equal.

For example: If two coffee cups are placed in a box where the temperature is 15 degrees Celsius, and then a third coffee cup with a temperature of 30 degrees celsius is added to the box, then the temperature of the first two coffee cups will increase to 20 degrees Celsius, and gradually, the temperature of the third coffee cup will also reach 20 degrees Celsius. 

Zeroth law demonstrates the concept of the motion of temperature.

Now, let’s understand the First law of thermodynamics. 

The first law of thermodynamics is also known as the law of energy conservation. 

The first law states that energy cannot be created nor destroyed, but it can be converted from one form to another form.

For example, the melting of an ice cube is a classic example of the first law of thermodynamics. When you leave an ice cube in the open, it will melt and turn into water in a few minutes. This happens because the ice absorbs heat from the surrounding air, which cools the air and changes the ice into water.

The formula for the first law of thermodynamics is ΔU=Q−W, where ΔU is the internal energy, Q is the heat, and W is the work.

Next, let’s understand the Second law of thermodynamics

Kelvin Planck and Rudolf Clausius gave their statements on the second law of thermodynamics. 

Kelvin Planck’s statement states that it is impossible to construct an engine whose only purpose is to convert heat from a source of high temperature into an equal amount of work.

In other words, it is difficult to create an engine that can convert heat into work completely. 

Rudolf Clausius’s statement states that heat cannot pass from a colder body to a warmer body without some other change occurring at the same time.

This means that energy cannot flow spontaneously from a colder body to a warmer body without any external intervention.

Finally, let’s look at the Third law of thermodynamics

The third law of thermodynamics states that as the temperature of a system approaches absolute zero, its entropy becomes constant, or the change in entropy is zero.

In conclusion, the laws of thermodynamics provide a fundamental understanding of the behavior of energy in physical systems. The first law states that energy cannot be created or destroyed, but only converted from one form to another. The second law asserts that in any energy conversion, some energy will inevitably be lost as waste heat. Finally, the third law establishes an absolute zero temperature that cannot be reached.

These laws have vast implications across many scientific disciplines, from physics and chemistry to biology and environmental science. They provide a framework for understanding energy flow, heat transfer, and the behavior of matter at the atomic and molecular levels.

Furthermore, these laws have practical applications in fields such as engineering, where they are used to design more efficient engines and power plants. They also inform our understanding of natural phenomena, such as the behavior of stars and the Earth’s climate.

Overall, the laws of thermodynamics represent one of the most important contributions to our understanding of the physical world. By describing the behavior of energy in all its forms, they provide a foundation for scientific inquiry and technological innovation.