# Understanding the 4 Laws of Thermodynamics: A Layman's Guide

• rjsniz
In summary, the conversation discusses the four laws of thermodynamics and their explanations. The first law states that energy cannot be created or destroyed in a closed system. The second law deals with entropy and states that the disorder of a system cannot decrease. The third law states that absolute zero temperature is impossible to reach. The zeroth law states that if two objects are the same temperature as a third object, they are also the same temperature as each other. The conversation also mentions the possibility of decreasing entropy by shuffling it to a different place.
rjsniz
Help! Wouls someone be so kind as to explain the 4 laws of thermodynamics in 'laymans terms', so that I could better understand them. A short but complete explanation would be appreciated!
Thanks.

There is a basic list here: http://www.health.uottawa.ca/biomech/csb/laws/thermos.htm

The 3 after zeroth are easy to remember.

You can't win

This is the law of energy conservation, or law number one. It states that in any closed system, you will always wind up with the same amount of energy you started with. For example, take X amount of matter, which has a certain rest energy amount. If you were to attempt to completely destroy the matter, it would merely be converted to another form of energy. (ie. heat, EM radiation) The total amount of energy from this heat would still be equal to the original amount the matter had. Basically, energy can neither be created nor destroyed. Hence the title, you can't win.

You can't break even

This is the second law dealing with entropy. The disorder of a system can never decrease. Take the example above of matter, for example. If you convert the matter into radiation, the total amount of energy in the system stays the same, but the potential energy has decreased. The radiation that carries the energy from the now absent matter cannot be used to do work. One example of entropy is the universe as a whole. As time goes by, most of the energy in the universe will be in the form of radiation, and cannot be used for work. Hence, the universe dies a "heat death" and humans are screwed.

You can't leave the game

The third law states that the temperature of absolute zero for a system is impossible. There was an article about this on Physics Post, at [Removed Broken Link]

The explanations above are not the most detailed, but maybe someone here can provide more insight.

Last edited by a moderator:
Eh's explanations are good.

One comment: The second law states that for a closed system entropy can never decrease.

It is certainly possible to decrease entropy by shuffling it to a different place. For example, a freezer freezing water. Ice has less disorder than water. To freeze it, you need to take the 'disorder' from the water and push it into a different place: The air outside the refrigerator.

The zero'th law is really simple.

If particle A is the same temperature as particle B, and particle B is the same temperature as particle C, then particle A is the same temperature as particle C.

The point is that there is a rule which governs thermometers. It's a 'duh' type statement, but the three laws have nothing in them which say that a thermometer which reads 20 degrees for one object will actually read 20 degrees for another object.

## What are the 4 laws of thermodynamics?

The first law states that energy cannot be created or destroyed, only transferred or converted. The second law states that the total entropy of a closed system will always increase over time. The third law states that the entropy of a perfect crystal at absolute zero is zero. The fourth law, also known as the zeroth law, states that if two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.

## What is the difference between the first and second laws of thermodynamics?

The first law deals with energy conservation, stating that the total energy in a closed system remains constant. The second law deals with the direction of energy flow, stating that energy will always flow from areas of high concentration to areas of low concentration, resulting in an overall increase in entropy.

## Why is the third law of thermodynamics important?

The third law establishes a reference point for measuring the absolute entropy of a substance. It also helps to explain why it is not possible to reach absolute zero temperature, as it would require a system to have zero entropy, which is impossible according to the third law.

## What are some real-world applications of the laws of thermodynamics?

The laws of thermodynamics have numerous applications in various fields, including engineering, chemistry, and biology. They are used to design more efficient engines, predict the behavior of chemical reactions, and understand the energy transfer in living organisms, among others.

## Are there any exceptions to the laws of thermodynamics?

While the laws of thermodynamics hold true in most situations, there are a few exceptions. For example, at the quantum level, particles can spontaneously appear and disappear, violating the first law. Also, in extremely low temperatures, some substances may exhibit negative entropy, violating the third law. However, these exceptions do not invalidate the laws of thermodynamics, but rather show their limitations in certain scenarios.

• Thermodynamics
Replies
4
Views
942
• Thermodynamics
Replies
13
Views
1K
• Thermodynamics
Replies
10
Views
2K
• Thermodynamics
Replies
4
Views
797
• Thermodynamics
Replies
2
Views
445
• Thermodynamics
Replies
1
Views
819
• Thermodynamics
Replies
13
Views
2K
• Thermodynamics
Replies
6
Views
1K
• Thermodynamics
Replies
8
Views
912
• Thermodynamics
Replies
2
Views
1K