# What is Free expansion: Definition and 36 Discussions

The Joule expansion (also called free expansion) is an irreversible process in thermodynamics in which a volume of gas is kept in one side of a thermally isolated container (via a small partition), with the other side of the container being evacuated. The partition between the two parts of the container is then opened, and the gas fills the whole container.
The Joule expansion, treated as a thought experiment involving ideal gases, is a useful exercise in classical thermodynamics. It provides a convenient example for calculating changes in thermodynamic quantities, including the resulting increase in entropy of the universe (entropy production) that results from this inherently irreversible process. An actual Joule expansion experiment necessarily involves real gases; the temperature change in such a process provides a measure of intermolecular forces.
This type of expansion is named after James Prescott Joule who used this expansion, in 1845, in his study for the mechanical equivalent of heat, but this expansion was known long before Joule e.g. by John Leslie, in the beginning of the 19th century, and studied by Joseph-Louis Gay-Lussac in 1807 with similar results as obtained by Joule.The Joule expansion should not be confused with the Joule–Thomson expansion or throttling process which refers to the steady flow of a gas from a region of higher pressure to one of lower pressure via a valve or porous plug.

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13. ### Thermodynamics -- Free expansion of gas

We have 2 (insulated) partitions, one with the gas, another vacuum, separated by a stop cock. We remove the cock, letting the gas expand into vacuum . I understand that since there is no opposing force on the expanding gas ,the work done by the gas is zero . But work done by gas is given by...
14. ### Why is the internal energy change of free expansion 0?

ΔU=q-w and in a free expansion w=0 and Free expansion is an irreversible process in which a gas expands into an insulated evacuated chamber. Does this mean that free expansion is an isolated system? Meaning the walls of the container are adiabatic in which no heat can enter the system and so q=0...
15. ### Why dU may not equals dW in free expansion?

From a video lecture, it is mentioned that "dU≠dW in Joule's free expansion if the process is irreversible and adiabatic" Mentioned in around 36:00-38:00 in the video: What I would like to ask is why in this irreversible adiabatic process, dU≠dW? Is it because the W here doesn't include other...
16. ### Adiabatic Free Expansion and Reversible Isothermal Path

Homework Statement Consider an ideal monatomic gas that undergoes an adiabatic free expansion starting from equilibrium state A with volume 500 cm3, pressure 40 kPa and temperature 300K to state B, which has a final equilibrium volume of 1000 cm3. Construct an reversible isothermal path that...
17. ### Free energy in the free expansion of an ideal gas

Hello PF! Consider the free expansion of an ideal gas. The process occurs at constant temperature, therefore, ΔU = 0, Q = 0, and W = 0. Suppose we are given the initial and final pressures of the gas, and we calculate ΔG = nRT ln(P2/P1). As P2 < P1, ΔG < 0. This is intuitive, as a free expansion...
18. ### Free expansion of a Van der Waals gas, physical explanation

Hello! Today I've learned that when a Van der Waals gas undergoes a free expansion, it cools down a bit. :bugeye: This is in contrast with the ideal gas in which case since it does no work and since the process is adiabatic, the internal energy of the ideal gas remains unchanged by the...
19. ### Free Expansion of Ideal Gas: Isothermal or Adiabatic?

Let's consider free expansion of an Ideal gas into vacuum. We have 2 (insulated) partitions, one with the gas, another vacuum, separated by a stop cock. I lift the cock, letting the gas expand into vacuum. I am aware that in free expansion of a gas into vacuum, the change in internal energy i.e...
20. ### Adiabatic Free Expansion Question

A typical free expansion scenario described in texts is that of a gas confined to a thermally insulated container with a removable membrane. When the membrane is removed the gas expands into vacuum. I understand that no work can be done because the gas does not exert a force. However, I am...
21. ### Thermodynamics problem: Adiabatic free expansion

Homework Statement A rigid ( ie. Constant volume), non-conducting ( ie. Perfectly insulated, no heat losses or gain) tank with a volume of 4.6 m^3. The tank is divided into two unequal parts by a thin membrane. One side of the membrane representing 1/3 of the tank is filled with nitrogen ( may...
22. ### Semi-idealized atomic gas and it's free expansion in vacuum

Hello! I was thinking about what would happen if an atomic gas was allowed to expand in vacuum and concluded I don't have much of a handle on the subject, so if anyone would help me out - I'd really appreciate it. So, let's say we have an ideal gas in a container located in vacuum...
23. ### Mostly Free Expansion of Ideal Gas

Hey All, Had a problem to solve and wanted to know how others would approach it. Problem is as follows: An insulated container of known volume has an orifice of know size. Container is filled with air and left to rest so that temperature and pressure is that of atmospheric surroundings...
24. ### Thermodynamics: proof about free expansion

Homework Statement prove that for a free expansion the following equality holds: \left( \frac{\partial T}{\partial V} \right) _{U} = - \frac{1}{C_{V}} \left[ T \left(\frac{\partial P}{\partial T} \right)_{V} - P \right]Homework Equations thermodynamic potentials, maxwell equations etc.The...
25. ### Free Expansion is non-spontaneous?

I searched in the fora, and I did find https://www.physicsforums.com/showthread.php?t=292278" asking pretty much the same thing. Internal energy change and work done are zero, so no heat is absorbed. Thus entropy is zero, hence it isn't spontaneous. What am I doing wrong? Could you also...
26. ### Entropy change in free expansion.

Suppose there are two parts in an insulated chamber, one filled with ideal gas and other is complete vaccum, separated by a partition. Now if partition is removed then gas will rush in other part to fill the whole chamber. PROBLEM- Now there should be increase in entropy of system but i have...
27. ### Free expansion and adiabatic process

I hope someone in here can help me out of this problem. I know that for calculating the change in entropy of a system (\Delta S) we can use this formula : \Delta S=\intδq/T Well the problem is here, when we calculating ΔS for an adiabatic process we know Q= 0 so ΔS=0 in this process, but...
28. ### Free expansion of a Van der Waal's Gas

Homework Statement There are two vessels connected by a stopper. Both have the same volume. One has "N_a" moles of gas, the other "N_b". Find the expression for the change in temperature when the stopper is opened and the system is allowed to come to a new equilibrium state. The...
29. ### Free expansion of a gas problem

Hello. This is my first post in this forum, so bear with me on any flaw or mistake please. Homework Statement Imagine a gas confined within an insulated container as shown in the figure below. The gas is initially confined to a volume Vi at pressure Pi and temperature Ti. The gas then is...
30. ### Free expansion of an ideal gas.

I know that the work done on the system in any free expansion is 0 since the external pressure is 0. However.. is q necessarily 0? Does the temperature necessarily stay constant for an ideal gas? I've been trying to justify the reasons for which q is necessarily 0, but I can't find a...
31. ### Work during free expansion of a gas

Hello, I have a small problem concerning the free expansion of a gas. https://www.physicsforums.com/attachment.php?attachmentid=20388&stc=1&d=1252066499 The two chambers are separated by a movable piston (without friction). Obviously the gas will expand because it puts pressure p on the...
32. ### Entropy variation during free expansion

Homework Statement A system that consists of n moles of ideal gas does a free expansion (to the vacuum) from a volume V to a volume 2V. a) What is the variation of entropy of the gas?; b) of the universe?; c) if the expansion was reversible and isothermal, what would be the variation of the...
33. ### Van der waal gas in isothermal free expansion

Homework Statement A gas obeys the Van Der Waal equation of state. The gas undergoes a free expansion from volume Vi to Vf at a constant temperature T. Find the change in entropy of the gas.Homework Equations du=Tds-Pdv+mdn The Attempt at a Solution I can solve the problem assuming du= 0 but...
34. ### What Happens During Free Expansion?

what happens in a free expansion?
35. ### Understanding the Limit of Irreversibility: Free Expansion Explanation

Why does free expansion represent the limit of irreversibility at which all of the "potential" work is degraded to heat.
36. ### Free expansion of an ideal gas

For the free expansion of an ideal gas into an evacuated chamber, I know that Work=0 and Q=0. Correct? This implies that the change in internal energy dU also equals 0. Since U depends solely on T, this should mean that the final temperature of the chamber is equal to the temperature of the...