# Questions tagged [entropy]

An important extensive property of all systems in thermodynamics, statistical mechanics, and information theory, quantifying their disorder (randomness), i.e., our lack of information about them. It characterizes the degree to which the energy of the system is *not* available to do useful work.

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### What is "order" and "disorder" in entropy?

What is "disorder" in entropy? Entropy is measurement of "disorder". (Some says it's not "disorder") I had read "disorder" and "order" of entropy in ...
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### Understanding entropy [duplicate]

I am currently doing some research on entropy and I am trying to get my head around the concept. One thing that I am getting right now is that entropy is just an application of probability and ...
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### What makes procesess internally reversible?

So I read that processes where there is no thermal gradients in the system are internally reversible, but for other cases, do we have to consider the temperature of boundary to calculate entropy ...
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### Is there any physical example of a real closed system?

Is there any physical example of a real closed system? I am aware that the whole universe can be considered as a closed system, but I am looking for a smaller example.
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### Finding energy of a rubber band

I'm solving a thermodynamics exercise and at one point I'm asked to find the energy if a rubber band. The rubber band has temperaturte $T$ lenght $L$ and tension $J$. I'm given the following ...
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### Entropy production rate due to heat transfer

I don't understand how you can derive a formula for the rate of entropy generation due to heat transfer between two sources with temperatures $T_2$ and $T_1$ without varying the temperature themselves....
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### Entropy: Disorder or energy dispersal?

The first definition of entropy given by Clausius is I believe this $$S=Q/T$$ It is as I understand a common fact to understand entropy and maybe often teach it as a measure of disorder through the ...
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### Thermal noise in suspensions of mesoscopic particles

By considering the steady state mean-squared-displacement of a particle undergoing Langevin dynamics in a harmonic potential well, Einstein was able to relate the diffusion constant of a colloidal ...
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### Paradoxical definition of equilibrium using entropy

I've read that equilibrium is the state at which entropy has a maximum. However I found this definition paradoxical because on books entropy is usually defined only for equilibrium states. How is it ...
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### Making sense of Entropy being energy over temperature

Over the internet, I found many resources that explain very well what entropy represents. However, the dimensions still appear hard for me to make sense of: energy, simply put, is the ability to do ...
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### Must the entropy change produced within a system always be greater than 0?

In McQuarrie's Physical Chemistry text the following is claimed in regard to a system's change in entropy: $$dS=dS_{exch}+dS_{prod}$$ That is, the system's change in entropy can be separated into a ...
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### Does $W_{out}$ in gas turbines refer to the shaft or the blades?

I was studying the Bryton cycle for a gas turbine and a question came to my mind about the turbine work output. That is, are we talking about the work output for the turbine blades or about the work ...
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### Irreversibility of heat transfer between two reservoirs

In a closed system the entropy change is given by $\Delta s=s_{gen}+\int \delta Q/T$. If $s_{gen}=0$, the state change is called reversible. Why is a heat flux between a hot and a cold reservoirs ...
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### Is falling in vacuum reversible or irreversible process?

Process is reversible if you can return to initial state through the same intermediate equillibrium states and cause infinitesimaly small changes in surrounding area. Does that mean that falling in ...
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### How is a irreversible process (conventionally) represented on a $T-S$ plane and why cannot it be (really) represented?

A reversible process can be represented on a $T-S$ plane, and the area under the curve is the heat exchanged by the system. On $P-V$ plane a irreversible process is conventionally represented with a ...
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### Boltzmann distribution as an explanation for the 2nd law of thermodynamics

The Wikipedia page for Boltzmann distribution describes it as a distribution of microstates as a function of energy and temperature. From my understanding, the 2nd law of thermodynamics is based on ...
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### Why doesn't the formula for the entropy change of an isobaric process include a work term?

I tried to derive the entropy change of an isobaric process and arrived at: $\Delta S = C_pln(T_2/T_1)+nRln(V_2/V_1)$ However, it appears the answer is just: $\Delta S = C_pln(T_2/T_1)$ It seems like ...
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### What is the entropy change due to work?

The equation $dS=\frac{dQ}{T}$ tells us the entropy change due to heat transfer. Likewise, the equation $dS=\frac{P}{T}dV$ tells us the entropy change due to a volume change. However, I am not sure ...