There are four laws of thermodynamics and are given below:
- Zeroth law of thermodynamics
- First law of thermodynamics
- Second law of thermodynamics
- Third law of thermodynamics
In the next few sections, we will discuss each of the laws of thermodynamics in detail.
Zeroth Law of Thermodynamics
The Zeroth law of thermodynamics states that if two bodies are individually in equilibrium with a separate third body, then the first two bodies are also in thermal equilibrium with each other.
This means that if system A is in thermal equilibrium with system C and system B is also in equilibrium with system C, then system A and B are also in thermal equilibrium.
An example demonstrating the Zeroth Law
Consider two cups A and B, with boiling water. When a thermometer is placed in cup A, it gets warmed up by the water until it reads 100 °C. When it reads 100 °C, we say that the thermometer is in equilibrium with cup A. When we move the thermometer to cup B to read the temperature, it continues to read 100 °C. The thermometer is also in equilibrium with cup B. By keeping in mind the zeroth law of thermodynamics, we can conclude that cup A and cup B are in equilibrium with each other.
The zeroth law of thermodynamics enables us to use thermometers to compare the temperature of any two objects that we like.
First Law of Thermodynamics
First law of thermodynamics, also known as the law of conservation of energy, states that energy can neither be created nor destroyed, but it can be changed from one form to another.
The first law of thermodynamics may seem abstract, but we will get a clearer idea if we look at a few examples of the first law of thermodynamics.
First Law Of Thermodynamics Examples:
- Plants convert the radiant energy of sunlight to chemical energy through photosynthesis. We eat plants and convert the chemical energy into kinetic energy while we swim, walk, breathe, and scroll through this page.
- Switching on light may seem to produce energy, but it is electrical energy that is converted.
Second Law of Thermodynamics
Second law of thermodynamics states that the entropy in an isolated system always increases. Any isolated system spontaneously evolves towards thermal equilibrium—the state of maximum entropy of the system.
The entropy of the universe only increases and never decreases. Many individuals take this statement lightly and for granted, but it has an extensive impact and consequence.
Visualizing the second law of thermodynamics
If a room is not tidied or cleaned, it invariably becomes more messy and disorderly with time. When the room is cleaned, its entropy decreases, but the effort to clean it has resulted in increased entropy outside the room exceeding the entropy lost
Third Law of Thermodynamics
Third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.
The entropy of a pure crystalline substance (perfect order) at absolute zero temperature is zero. This statement holds true if the perfect crystal has only one state with minimum energy.
Third Law Of Thermodynamics Examples:
Let us consider steam as an example to understand the third law of thermodynamics step by step:
- The molecules within it move freely and have high entropy.
- If one decreases the temperature below 100 °C, the steam gets converted to water, where the movement of molecules is restricted, decreasing the entropy of water.
- When water is further cooled below 0 °C, it gets converted to solid ice. In this state, the movement of molecules is further restricted and the entropy of the system reduces more.
- As the temperature of the ice further reduces, the movement of the molecules in them is restricted further and the entropy of the substance goes on decreasing.
- When the ice is cooled to absolute zero, ideally, the entropy should be zero. But in reality, it is impossible to cool any substance to zero.
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