Why Second Law of Thermodynamics is Needed? (2 Reasons)

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There are two main reasons why second law of thermodynamics is needed or important.

  • Second law of thermodynamics is used to check whether the process is spontaneous or not. (Whether the process occurs on its own or not?)
  • It also tells us the direction in which the process will proceed.

Let’s take an example of hot coffee to understand why we need the second law of thermodynamics.

Why Second Law of Thermodynamics is Needed

Just imagine, what happens when you keep the hot cup of coffee in an open room?

The coffee will cool down. Right?

In thermodynamics, we say that heat has transferred from the higher temperature body (coffee) to the lower temperature body (surrounding air of room).

And this process occurs on it’s own.

But what about the reverse process?

Will the heat of the room be transferred back to the cup of coffee?

Well, the first law of thermodynamics says that this process is possible.

Energy can be transferred from one form to another.

According to the first law of thermodynamics, the heat energy of the room can be transferred back to the coffee. But in actual practice it is not possible to have such a process taking place on it’s own. 

You know that, right?

This is only the limitation of first law of thermodynamics, that it does not describe the direction of the process. 

In our example of coffee cup, the first law fails to say whether the spontaneous heat transfer takes place  from coffee to the room or from room to the coffee?

In order to overcome this limitation of first law of thermodynamics, the second law of thermodynamics was discovered. 

Thus, 

  • Second law of thermodynamics is used to check whether the process is spontaneous or not. (Whether the process occurs on its own or not?)
  • It also tells us the direction in which the process will proceed.

(If you don’t know about the first law of thermodynamics, then kindly visit this first law of thermodynamics from here.)

I hope you have come to know why the second law of thermodynamics is important.

For more detailed information on Second law of thermodynamics, check the ultimate guide on Second law of thermodynamics.

(This guide has all the important knowledge about Second law of thermodynamics along with real life examples and lots more. You will love this guide for sure.)

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