Entropy
Entropy
(an explosion is a great example of an increase in disorder)
Entropy can be defined as the measure of dissorder a system contains. One way to calculate entropy is to use a formula Ludwig Boltzman came up with:
S = k ln W
Where k is Boltzman's constant : k = 1.381 * 10-23 J/K
W represents the number of different ways in which energy of a system can be rearranged.
Entorpy deals with last two laws of thermodynamics and the Nernst Heat Theorem.
Second Law of Thermodynamics:
The entropy of an isolated system increases in the course of a spontaneous change:
Stot > 0
where Stot is the total entropy of the isolated system that contains the system of intrest.
Third Law of Thermodynamics:
If the entropy of every element in its most stable state at T=0 is taken as zero, then every substance has a positive entropy which at T=0 may become zero, and which does become zero for all perfect crystalline substances, including compounds.
Nernst heat theorem:
The entropy change accompanying any physical or chemical transformation approaches zero as the temperature approaches zero: as the temperature approaches zero the change in entropy approaches zero.
Here are some examples of entropy:
Why does a cold glass of lemonade become warm on a hot day? What is happening is a transfer of energy (heat) from the surroundings to the glass of lemonade. So that, the glass of lemonade increases in entropy (disorder, increased molecular movement) as the surrounding air decrease in entropy. The incease in entropy must equal the decrease in entropy.
How does an ice cube's melting deal with entropy? As an ice cube melts it changes states. To change state the ice cube's molecules must increase in activity. This increase is an increase in disorder or losely defined an increase in entropy.
Entropy is a tricky thing to define but maybe some of these links below will help give you a better grasp of this concept.
( definitions taken from Atkins, P. "Physical Chemistry 5th Ed.", 1994)
A famous chemist that worked on determing entropy was W.F. Giauque. He proved that entropy is a natural law. As one of our projects for the semester we wrote a paper on a paper that Giauque wrote. If you click below you can read my paper that deals with Giauque's determination of entropy at low temperatures for hydrogen sulfide.
The Page of Entropy ( this page has some good definitions and examples)
Entropy (some cool pictures for understanding entropy)
2nd and 3rd Law of Thermodynamics
Augustana College Home Page: Chemistry
The College of Chemistry UC Berkeley (Giauque's old school)
The World-Wide Web Virtual Library: Chemistry
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