Physics Help Forum Why entropy is more if heat is more?

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 Oct 15th 2017, 12:50 AM #1 Senior Member     Join Date: Feb 2017 Posts: 205 Why entropy is more if heat is more? As we know what heat is. Heat is molecules having more kinetic energy. Kinetic energy increases as an object gets hotter. So hotter object has more energy i.e kinetic energy. So with more energy there are more possible arrangement of the molecules so entropy is more. Does this mean as an object gets hotter there are more ways molecules can be arranged? Is entropy the number of arrangements of a molecule?
Oct 15th 2017, 01:28 AM   #2
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 Is entropy the number of arrangements of a molecule?
No, we are back to the jigsaw question.

The physical arrangements do not contribute to entropy.
They can serve as a model for the statistics.

Given a specific number of energy states, it is the distribution of the participants over these energy states that creates the entropy.

Change this distribution and you will change the entropy.

 Heat is molecules having more kinetic energy.
Yes some added heat may become (increased) molecular kinetic energy.
But this KE also contributes to the pressure.

Additionally the heat may cause other effects such as thermal excitation of the vibrations of the molecule, thermal ionisation and so on.

Heat is not a property of the system it is the transfer of energy. (but remember there are other modes of energy transfer, can you name one ?)
Enthalpy is the state property of the system that is the nearest to the idea of heat.

Last edited by studiot; Oct 15th 2017 at 01:33 AM.

 Oct 15th 2017, 04:03 AM #3 Senior Member     Join Date: Feb 2017 Posts: 205 Entropy Lets assume someone had a doubt and he googled, luckily he got to see this thread. After reading this thread he thought over it. Now he wants to know what is entropy. So lets help him out. Studiot said "Given a specific number of energy states, it is the distribution of the participants over these energy states that creates the entropy". What is an energy state? According to me it means microstate. Lets see what is a microstate. Consider the general case of a system comprised of N particles distributed among n boxes. The number of microstates possible for such a system is n^N. For example, distributing four particles among two boxes will result in 2^4 = 16 different microstates. So there are 16 possible distributions which means 16 microstates. Microstates are nothing but total number of distributions. Last edited by avito009; Oct 17th 2017 at 12:47 AM.
Oct 15th 2017, 04:13 AM   #4
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 Originally Posted by avito009 Lets assume someone had a doubt and he googled, luckily he got to see this thread. After reading this thread he thought over it. Now he wants to know what is entropy. So lets help him out. Studiot said "Given a specific number of energy states, it is the distribution of the participants over these energy states that creates the entropy". What is an energy state? According to me it means microstate. Lets see what is a microstate. Consider the general case of a system comprised of N particles distributed among n boxes. The number of microstates possible for such a system is n^N. For example, distributing four particles among two boxes will result in 2^4 = 16 different microstates.
Whether the energy state is a microstate or a macrostate depends upon the details of the analysis.

When a solid melts is gains the entropy of fusion.
This is a macrostate.

Your example of things in boxes is an example of spatial arrangement that is not entropy.

Although the statistical definition of entropy is a very simple equation,
Calculating entropy from statistics is more difficult because, as you have realised, you have to identify and quantify all the states and then perform the integration of the equation.

Entropy is widely very poorly taught at the introductory stage, which leads to far too much semi mystical nonsense about it.
There is a very simple, easy to understand classical way to treat it, I don't know why that way is not taught more often.

 Oct 17th 2017, 12:53 AM #5 Senior Member     Join Date: Feb 2017 Posts: 205 Alternate formula of entropy. When we are talking about entropy as disorder. I think the correct formula for that would be this: S=klnΩ Entropy is a logarithmic tally of the number of microscopic states. It means entropy is directly proportional to microstates of a system. Entropy is really a measure of the system disorder; the more particles we have, the more possible arrangements we have, and essentially the more mess we can make. The more the microstates of a system more is the disorder. Last edited by avito009; Oct 17th 2017 at 02:06 AM.
Oct 17th 2017, 03:15 AM   #6
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 Originally Posted by avito009 When we are talking about entropy as disorder. I think the correct formula for that would be this: S=klnΩ Entropy is a logarithmic tally of the number of microscopic states. It means entropy is directly proportional to microstates of a system. Entropy is really a measure of the system disorder; the more particles we have, the more possible arrangements we have, and essentially the more mess we can make. The more the microstates of a system more is the disorder.
You seem to be having trouble with this concept.

The states referred to are energy states.

They are not configuration states.

Consider a single molecule, bouncing around inside a box.

Is the entropy any different when it is in the left hand half of the box or the right hand half of the box or the middle?

Or here is another way to look at it. Can you tell me the units of entropy?

Last edited by studiot; Oct 17th 2017 at 03:20 AM.

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