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Name: Linda G.
Status: educator
Age: N/A
Location: MO
Country: N/A
Date: N/A

I need a simple definition of entropy and the three laws of thermodynamics. I do teach middle school but the simpler the better.

First cannot win
Second cannot break even
Third will always lose in the game

All things tend to chaos...disorder...Entropy is the law that which governs the order of their lockers and their bedrooms, your matter what we do it they always seem to get messy...we have to continuously expend energy to keep them orderly.

Peter Faletra

Hi Linda,

Entropy: the amount of disorder in a system. Disorder increases, entropy increases. Tell the kids to think of their rooms. You get it cleaned and by the end of the week, if they are like most kids, it needs to be cleaned and picked up again. A teenager's bedroom is a study in entropy.

First Law: Whenever heat is added to a system, it transforms to an equal amount of some other form of energy.

This added energy does one or both of two things: (1) Increases the energy in the system and (2) does external work if it leaves the system.

(Conceptual Physics, Paul Hewitt, Pub. by Scott Foresman Addison Wesley, 1999 edition)

2nd Law Heat will NEVER flow from cold to hot within a system. It always goes from hot to cold. Touch a piece of metal , hold it, it warms up, your hand seems cooler. Heat is flowing from your warm hand to the metal.

I hope this helps,
Martha Croll


1st Law: The internal energy of an isolated system is constant.

[translation: if the system is not losing heat, gaining heat, doing work, or being worked on, it is isolated. In other words, if it is not touching the world in any way, its energy is not changing]

2nd Law: The entropy of an isolated system increases in the course of any spontaneous change

[translation: the natural progression of the universe is from order to disorder]

My favorite example of entropy is my bedroom. I can clean it, but it always gets messy again-->it is the natural progression of the universe. ;) This is entropy. The easiest way to think of entropy is disorder.

3rd Law: All entropies of all perfect crystals are the same at the absolute zero of temperature.

[translation: at absolute zero there is NO energy, and therefore the atoms in a crystal do not move at all. If they are not moving, there is no tendency towards disorder. At all other temperatures, atoms in a crystal lattice are still moving (vibrating)

At the University, the two laws we put the most empahsis on in the general chemistry courses are the 1st and 2nd.

Hope this helps.

---Michelle Weinberger

P.S. The definitions of the laws as cited here are taken from "Chemical Principles: The Quest for Insight" 2nd edition by Peter Atkins and Loretta Jones The "translations" are entirely my doing....


I do not know if these are simple enough, if not, maybe reply to this and we will give it another go.

The First Law of Thermodynamics is simply a conservation of energy law. This means that energy is neither created nor destroyed. Energy is just transformed from one form to another.

The Second Law of Thermodynamics states that when things happen spontaneously (such as a water evaporating, or the library become more disorganized when students use it, or water spreading on the surface of a table) this always means that that thing is getting more disorganized.

The Third Law of Thermodynamics is simply a statement that we understand that the degree of disorganization within objects can be measured (referenced to a theoretical object that has zero disorganization).

There is also the Zeroth Law of Thermodynamics which is basically stating that we can measure temperature - because when objects come into contact to each other, they tend to, or eventually, get to the same temperature.

Greg (Roberto Gregorius)

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