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Explain Entropy? 7
- Thread starter Rpsfinest
- Start date
Here's an introduction. The ice water example is a common one.
Hello everybody:
This site can help you.
This site can help you.
Entropy is simply the amount of energy in something at a given condition.
A common application is in steam power systems.
The conditions (temperature, pressure) of steam entering and exiting a turbine are known.
Look up the entropy for those conditions. The difference in energy is assumed to have been converted to useful work in the turbine.
A common application is in steam power systems.
The conditions (temperature, pressure) of steam entering and exiting a turbine are known.
Look up the entropy for those conditions. The difference in energy is assumed to have been converted to useful work in the turbine.
There are many definitions of entropy as shown in the given links and posts, especially those associated with order and disorder.
The one I like concerns thermo.: An increase in entropy always corresponds to a degradation in energy quality, in that some energy becomes unavailable to do work. Meaning that entropy provides a measure of energy quality.
We could add that ireversible processes in which total energy remains constant, the deterioration of energy quality gives us a measure of the entropy change.
Given two systems with the same energy content, the one with the lower entropy contains the highest quality energy.
Living things and societies represent the organization of matter (entropy decreases) in an universe governed by a tendency toward disorder (entropy increases), come into being by getting high-quality energy from outside and at the expense of greater entropy increases elsewhere in the universe.
They don't escape the second law of thermodynamics: the entropy of the universe can never decrease.
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FredGarvin
Mechanical
That's probably the best explaination and the one I agree with the most. It's the one that is also easiest to put a physical connection to in my mind.
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Entropy is a property, just as is P, T, U, H, but it is not directly measurable- it might be considered to be a synthetic property. It was defined or created as part of the developement and statement of the 2nd law of thermodynamics. Simply defining and recognizing the conservation of energy (1st law) does not provide any clue as to which direction a process will proceed- but the 2nd law does define which is a likely or possible direction in which a process will proceed.
Consider the case of 2 items coming in contact with each other, but eaach at a different temperature. The 1st law does not define in which direction the heat will flow, but the 2nd law defines that the heat will flow from the hoter body to the colder body.
Another case: a bottle of gas is opened in a closed room. The first law will not predict that the gas will mix with the air in the room, but the 2nd law does predict that process. By the same token, the 2nd law would explain why the N2 and O2 in air will not spontaneously seperate from air and flow all by themselves into 2 seperate containers, although such a process is permitted by teh 1st law.
Likewise, when you burn gas in your car and the exhaust gas leaves the tailpipe and the extra lost heat is emitted tot he radiator, that direction of that process follows the 2nd law- although the 1st law would equally allow the reverse to occur- the exhaust gas return up the tail pipe, the heat to flow from radiator to engine block, and new gasoline to be formed in the cylinders. Basically, the 2nd law prevents things from operating backwards compared to our normal experience.
Consider the case of 2 items coming in contact with each other, but eaach at a different temperature. The 1st law does not define in which direction the heat will flow, but the 2nd law defines that the heat will flow from the hoter body to the colder body.
Another case: a bottle of gas is opened in a closed room. The first law will not predict that the gas will mix with the air in the room, but the 2nd law does predict that process. By the same token, the 2nd law would explain why the N2 and O2 in air will not spontaneously seperate from air and flow all by themselves into 2 seperate containers, although such a process is permitted by teh 1st law.
Likewise, when you burn gas in your car and the exhaust gas leaves the tailpipe and the extra lost heat is emitted tot he radiator, that direction of that process follows the 2nd law- although the 1st law would equally allow the reverse to occur- the exhaust gas return up the tail pipe, the heat to flow from radiator to engine block, and new gasoline to be formed in the cylinders. Basically, the 2nd law prevents things from operating backwards compared to our normal experience.
A useful practical explanation I've come across can be seen via the following link:
While the first law speaks of energy conservation, the second law (2LOT) teaches us that in the macroscopic world, where friction and other energy-dissipation mechanisms are present, a completely reversible process is an idealization that cannot be realized.
The 2LOT differs from most physical laws in being fundamentally statistical in that it rules out events not because they violate basic laws of mechanics but because they're simply too improbable.
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