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Laws of Thermodynamics
Name: Linda G.
Status: educator
Age: N/A
Location: MO
Country: N/A
Date: N/A
Question:
I need a simple definition of entropy and the three
laws of thermodynamics. I do teach middle school but the simpler the
better.
Replies:
First law...you cannot win
Second law...you cannot break even
Third law...you 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 classroom...no 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
Linda,
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....
Linda,
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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Update: June 2012
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