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To: betty boop

Entropy isn't easy to describe. You need to go through a beginning thermodynamics book mostly. However, that's never stopped me from posting, so here's a short description.

In any heat engine (automobile, for example) one does work by absorbing energy at one temperature (the combustion in the cylinder) and discharging heat at another (the exhaust, the cooling mainfold.) Some of this energy is converted to work (pushing the piston) but the rest is "waste" (from the point of the automobile.

The first law of thermodynamics basically says that the engine won't work if no energy is put into it (it's out of gas, for example.)

The second law says that all of the energy in the gas cannot be extracted to do work. Some of the energy must be wasted. Entropy is a variable that gives a quantitative measure of how much energy will be available or wasted.

Mathematically, one gets the equation: Free Energy (two types, named for Gibbs and Helmholtz; this is what's available for usefule work) equals the total energy input (enthalpy to use the technical term) minus the temperature times the entropy or: G=H-T*S. Entropy is a variable that has the same ontological status as heat or temperature.

You might surf the net looking for a popular explanation of the "Carnot cycle."


181 posted on 05/07/2005 8:36:28 PM PDT by Doctor Stochastic (Vegetabilisch = chaotisch is der Charakter der Modernen. - Friedrich Schlegel)
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To: Doctor Stochastic
Thanks so much for your excellent post, Doc. Could I ask you to indicate to me (and the Lurkers!) the differences re: the Gibbs and the Helmholtz varieties of Free Energy? My understanding of the Gibbs -- which is probably incorrect -- is that it is the result of chemical bonding, liberating "free electrons." I haven't come across the Helmholtz, however....

Thanks, Doc!

187 posted on 05/09/2005 11:04:22 AM PDT by betty boop (If everyone is thinking alike, then no one is thinking. -- Gen. George S. Patton)
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