Gas flows from cylinder A to cylinder B

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Homework Help Overview

The discussion revolves around the behavior of gas in two connected closed cylinders, A and B, with differing initial pressures and temperatures. Participants explore the implications of opening a valve between the cylinders and the resulting equilibrium state regarding pressure and temperature, while assuming no heat exchange with the surroundings.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants present differing views on whether the temperatures of the two cylinders will equalize when pressures are the same. Some reference the ideal gas law, while others consider the effects of flow work and energy conservation. Questions arise about the initial conditions, such as whether the pressures are gauge or absolute, and how these affect the outcome.

Discussion Status

The discussion is active, with participants questioning assumptions and exploring various interpretations of the problem. Some guidance is offered regarding the implications of flow work and energy conservation, but no consensus has been reached on the temperature behavior post-equilibration.

Contextual Notes

Participants note the potential confusion regarding the type of pressure measurements (gauge vs. absolute) and discuss the implications of starting conditions on the final state of the system. There is also mention of the kinetic energy of the gas molecules and its conversion to thermal energy.

mune
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Hi all,

Let's say we have 2 closed cylinders A and B, same volume, containing air inside. Two cylinders are connected to each other with a tube, with valve. Initially the valve is closed.

cylinder A: P=100 Pa, T= 350 k.
cylinder B: P=50 Pa, T= 300 k

now if the valve is opened, and closed when their pressure are the same.

assume no heat loss to or gain from surrounding.here my problem:
will their temperature be the same when their reach the same pressure?

my guess are...

1. yes. By ideal gas law, PV/T = mR, if P1=P2, V1=V2, then T1=T2, so the temp will be the same.

2. no. When the valve is opened, the air flows from A to B, which means the air does some flow work. By conservation of energy, the temp in B will be higher than A.

which one of me should I believe??

thanks.
 
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When A and B become (A+B), and it's adiabatic, what is the equilibrium state.

Certainly the pressure will equilibrate, but what can be said of the temperature?

the temp in B will be higher than A.
How? B is starting at a lower temperature than A. How could B end up at a higher temperature?

Those are lower pressures btw. Are those gage or absolute pressures?

Remember that 1 atm = 14.7 psi = 101.325 kPa.
 
Last edited:
what if they started with the same temperature, other condition remains the same?

assume the values are gage pressure values(but does make any difference?)
 
what if they started with the same temperature, other condition remains the same?
Then they remain at the same temperature. At some point in time, the pressures have to equilibrate.

assume the values are gage pressure values(but does make any difference?)
I'm thinking along the lines of PV=nRT, in which the pressure is in absolute terms.

Perhaps the pressures are in absolute, in which case, they are partial vacuums, or at least very low pressures.
 
what about the flow work? the air molecules which flow from A to B have some KE right? The KE will change into thermal E after the valved is closed?
 

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