0
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3answers
49 views

Does the entropy of an adiabatically isolated system stays the same after we decrease/increase the pressure?

Even if the system is isolated and there is no heat exchange with surroundings, shouldn't the decrease/increase of pressure result in increase/decrease of entropy? Does this property of an ...
1
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1answer
52 views

How to understand the indeterminate process in thermodynamics?

Consider a closed composite system with an internal movable adiabatic wall. If we release the piston, thermodynamics cannot determine the final equilibrium state (the temperature cannot be ...
5
votes
3answers
78 views

Can we apply $pV^\gamma$=const only for quasistatic adiabatic process?

But If this is so, I have often seen people applying this formula for quick processes where no heat exchange is possible. Here is an example from where I am quoting the following: we will assume ...
2
votes
1answer
149 views

Formula for molar specific heat capacity in polytropic process

I found this formula for a polytropic process, defined by $PV^n = {\rm constant}$, in a book: $$C = \frac R{\gamma-1} + \frac R{1-n} $$ where $C$ is molar specific heat and $\gamma$ is adiabatic ...
4
votes
2answers
81 views

Why is adiabatic process isentropic?

I have read that adiabatic process is isentropic because there is no heat exchange in an adiabatic process and thus no change in entropy. But my question is - Even in adiabatic process, work can be ...
0
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0answers
38 views

Adiabatic Expansion with expanding control volume

I have a tube with a length "L" and diameter "d" that is open on 1 side . At a certain point ( say "x" ) from the closed end of the tube, I have a gas with a high pressure. At this point, "x", there ...
3
votes
1answer
135 views

How do you explain the fact that when air expands freely into an evacuated chamber from a constant pressure atmosphere, its temperature increases?

I came across this paper: Baker, B. (1999). An easy to perform but often counterintuitive demonstration of gas expansion. American Journal of Physics, 67(8), 712-713. ...
6
votes
5answers
473 views

How is this process not quasi-static yet reversible?

Consider a (adiabatic) canister with a piston containing some gas kept in a vacuum. There are two weights on the canister which equalize the pressure of the gas on the piston. Assume the system is at ...
2
votes
0answers
301 views

Basic Thermodynamics: Quasistatic Adiabatic Process

I'm going through the exercises in a Thermodynamics book, just to revise and build my intuition. Right now, I'm working on: Show that for a quasistatic adiabatic process in a perfect gas, with ...
1
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1answer
51 views

Function describing an adiabatic process

I understand that an isothermic process, plotted on a PV diagram, can be described by a rectangular hyperbola. However, now I am wondering, what about an adiabatic process, what function best ...
0
votes
0answers
17 views

Work of an adiabatic/ compresion: sign?

As far as I am concerned the adiabatic work it is given by: $$ W_{adi}=\frac{P_{f}V_{f}-P_{i}V_{i}}{\gamma -1}$$ While I have seen in other examples that it is used with $1-\gamma$ in the ...
1
vote
1answer
384 views

Adiabatic proccess and Carnot cycle in a photon gas

I am making a comparation between the photon gas and the ideal classic gas for my Thermodynamics class. The photon gas is defined by the equations: $$U=aVT^4 $$ $$P=\dfrac{1}{3}aT^4$$ I found this ...
0
votes
2answers
636 views

How do you calculate the change in temperature of an adiabatic system?

I really don't even know how to start doing this problem. I understand PV=nRT and I understand that if either T, V, or P is kept constant, then the other 2 change at the same rate, and I understand ...
5
votes
1answer
624 views

Adiabatic expansion in van der Waals gas

Given a Van der Waals gas with state equation: $$\left( P+\frac{N^2 a}{V^2}\right)\left( V-Nb \right)=NkT,$$ show that the equation of an adiabatic process is: $$\left( ...
3
votes
2answers
2k views

Are reversible adiabatic processes always isentropic?

If my understanding is correct, neither reversible nor adiabatic processes are necessarily isentropic. But are reversible adiabatic processes always isentropic?
1
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1answer
136 views

Why is there a sign error in my derivation? Adiabatic expansion of ideal gas: $TV^{1-\gamma}$ is constant

This is the last part of a derivation of the equation for an ideal gas undergoing reversible adiabatic expansion. I'm trying to prove that $T V^{\gamma-1}$ is constant, but my result is that $T ...
1
vote
2answers
322 views

Adiabatic filling of a container

Suppose a thermally insulated container is filled with atmospheric air until the pressure reaches 5000 psi. This could represent the filling of a diving cylinder, before thermal dissipation becomes ...
0
votes
0answers
15 views

Calimetric Perfect Ideal Gas

What is the energy equation when you have a ridgid adiabatic open system where you have a mass flow rate in and a mass static inside the system?
0
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0answers
231 views

How does the volume change affect an adiabatic process?

A gas consisting of rigid diatomic molecules was initially under standard conditions. Then the gas was compressed adiabatically, 5 times the original volume. Find the mean KE of rotating molecules ...
2
votes
1answer
330 views

What defines the adiabatic flame temperature?

What defines the adiabatic flame temperature? In a case I have to solve, I need to describe the combustion of natural gas (Groningen natural gas, to be specific). However, I am having some problems ...
1
vote
2answers
971 views

How is it possible to equate the internal energy at constant volume with the internal energy of an adiabatic process?

I hope my question makes sense. My problem is that, I have read through numerous textbooks that nC(cons. volume)dT = -PdV when deriving the relationship between T and V for an adiabatic process, ...
12
votes
3answers
740 views

The notion of an adiabatic process in thermodynamics -vs- quantum mechanics

I'm confused about the terminology in the two contexts since I can't figure out if they have a similar motivation. Afaik, the definitions state that quantum processes should be very slow to be called ...
5
votes
1answer
331 views

Thermo homework (HW) problem

I do not believe this question can be solved with the thermodynamics knowledge that I have learned thus far, but someone correct me if I am wrong: A 0.2-m³ tank containing helium at 15 bar and ...
0
votes
1answer
1k views

Adiabatic expansion of steam through a valve

I'm working on a homework problem, and I have a suspicion the textbook is trying to trick me. The question is: "Steam at 20 bar and 300 C is to be continuously expanded to 1 bar. Compute the ...
2
votes
1answer
686 views

Isentropic Processes

I'm having trouble understanding why reversible adiabatic processes are isentropic. I understand that in a reversible adiabatic process there is no heat exchange and so $dQ = TdS = 0$. However, if ...
1
vote
1answer
831 views

Adiabatic expansion [closed]

I'll start off by saying this is homework, but I ask because I don't understand how the math should work (I don't just want an answer, I'd like an explanation if possible). I understand if this is ...
2
votes
2answers
463 views

Is it Possible to have Adiabatic Processes other than $PV^\gamma$ for the ideal Gas?

Is it possible to represent an adiabatic process for an ideal gas by a formula other than $PV^\gamma=Const$?: Relevant Considerations: We always need to connect a pair of arbitrary points/states ...
2
votes
2answers
8k views

Why does a gas get hot when suddenly compressed? What is happening at the molecular level?

My guess is that the molecules of gas all have the same speed as before, but now there are much more collisions per unit area onto the thermometer, thus making the thermometer read a higher ...
13
votes
4answers
1k views

How slow is a reversible adiabatic expansion of an ideal gas?

A truly reversible thermodynamic process needs to be infinitesimally displaced from equilibrium at all times and therefore takes infinite time to complete. However, if I execute the process slowly, I ...