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Fool wrote: ↑Sat Oct 05, 2024 6:04 am .

Tom Booth wrote: IMO gas molecules absolutely must have attractive forces that cause the group of molecules within a container or wherever, to come closer and closer together due to mutual attraction before finally coming close enough to condens into a liquid.

Molecules have a mutual attractive force. True. Gas molecules have relative velocities. If that velocity is above the 'escape velocity' they are gaseous. Below the escape velocity they tend to clump/liquefy. As two molecules get closer their mutual attraction makes their velocities increase. They accelerate towards each other. They get faster. Velocity is related to temperature. The funny thing is that escape velocity is higher when closer. So if below escape velocity, they tend to clump no matter how close they get or speed up from mutual attraction. If below the escape velocity, and they are clumping, they get close enough to have their repulsion kick in and effectively orbit each other, become liquid. Colder, they become solids, orbits become vibrations locked into positions.

There are several types of molecular bonding: ionic, covalent, Vanderwal, metallic, and hydrogen are some. They all have different strengths. Combined with size and pressure they dictate melting and boiling points.

If they are above the escape velocity, even if they are headed straight at each other, they will not clump. They will bounce off from each other's repulsive force, and keep going. This is true of identical molecules or different substances. They tend to trade energy's. Like a Newton's cradle. Trading kinetic energy is the transfer of heat. Heat is not the movement of molecules as often stated. Movement of molecules is internal energy, it is related to temperature. The attractive force, and repulsive force become transparent, and both are replaced by the bouncing force associated with energy and momentum.

The bouncing force added up is called pressure. There is talk of zero pressure in a vacuum, but it never quite gets there.

The velocity added up is called temperature. There is talk of zero temperature, but it never quite gets there

The range of travel, distance, is called volume. There is talk of zero volume in a vacuum, or at zero Kelvin, for an ideal gas, but never for a real gas. Real gasses have finite liquid and solid volumes.

Gasses don't liquefy because they get closer together, they liquefy because they get colder, slower. Pushing them together does increase that liquefaction temperature, but it increases temperature too. So pushing them together isn't likely to liquify them, unless cooled too.

So gases always push, are always present even when the liquid is smaller than the size of the container and also true of solids. That push just gets smaller, but never zero, even at very low temperatures. There is a sudden lowering change in pressure when a gas liquefies, (Can crush). Not so much when going from liquid to solid, but some can produce dramatic events, (Ice bomb).

Tom Booth wrote: As water vapor in a 55 gallon drum will condense (contract, draw together) into a liquid leaving a vacuum, so all gas molecules have mutual attraction and "contract", long before condensing into a liquid.

Yes. It is just overridden by the bounce force caused by being over the escape velocity, being hot and gasified.

Tom Booth wrote: Or do you suppose that a large volume of gas just suddenly ALL turns into a liquid without a gradual attraction drawing them closer and closer before finally condensing?

Yes. Except that gas molecules are always flying around each other, getting closer, bouncing off walls, bouncing off each other, getting further away, until they get cold enough, slow enough, to effectively spiral in, to an orbit. Example, cloud in a bottle.

https://m.youtube.com/watch?v=WeXuKd0vMRk

It may be the wrong video. I just copied it. Didn't watch it. Cloud forms suddenly by all the alcohol vapor turning suddenly into liquid droplets, no longer pushing, or pulling.


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Fool wrote: ↑Sat Oct 05, 2024 6:04 am ....
If they are above the escape velocity, even if they are headed straight at each other, they will not clump. They will bounce .... They tend to trade energy's. Like a Newton's cradle. Trading kinetic energy is the transfer of heat. Heat is not the movement of molecules as often stated. Movement of molecules is internal energy, it is related to temperature. The attractive force, and repulsive force become transparent, and both are replaced by the bouncing force associated with energy and momentum.

The bouncing force added up is called pressure. ....

Tom Booth wrote:Personally, I think condensation of water molecules in a 55 gallon drum is probably very gradual, just like condensation on the outside of a glass of ice water or lemonade on a hot summer day.

Flexi Says: The average distance a gas molecule travels between collisions is known as the mean free path. The exact distance varies depending on factors such as the temperature, pressure, and type of gas. However, for air at room temperature and atmospheric pressure, the mean free path is approximately 68 nanometers.

Google AI wrote:For a substance to exist as a gas, its molecules need to be moving at a speed where they can overcome the intermolecular forces holding them together, which typically requires an average molecular speed in the range of hundreds of meters per second depending on the substance and temperature involved; the exact speed depends on the molecule's mass and the temperature

Tom Booth wrote:Many gases certainly do condense under pressure without cooling. You apparently don't know much about the history of the liquefaction of gases.

Tim Booth wrote:Newton's Cradle, the actual device or demonstration model with the metal balls is far from the kinetic theory picture of gas molecules in random motion at high velocity. You elsewhere talk about "escape.velocity", so which is it?

Fool wrote: ↑Sun Oct 06, 2024 6:27 am

Tom Booth wrote:Personally, I think condensation of water molecules in a 55 gallon drum is probably very gradual, just like condensation on the outside of a glass of ice water or lemonade on a hot summer day.

I can agree with that. At 4 in the morning it's hard to say everything correct. It's always been my contention that barrel and can crushing is more a factor of container resistance change. Weaker as it begins to crush.

I don't see how a ball pit is analogous to a gas, but I do see the comparison to a pool of water.

What you are thinking about, is mean free path. How far a gas molecule travels before bouncing off another.

I googled it and got the following to come up.

Flexi Says: The average distance a gas molecule travels between collisions is known as the mean free path. The exact distance varies depending on factors such as the temperature, pressure, and type of gas. However, for air at room temperature and atmospheric pressure, the mean free path is approximately 68 nanometers.

It suggests that the mean free path gets longer as the pressure drops and temperature rises. I'm wondering how the distance relates to density. Density is related to closeness and size of molecule.

Solid is locked in crystallin form with vibration.

Liquid allows flow of molecules, but still bonded with vibration.

Gas has a separation, no longer bonded with free path and ability to escape. It must be contained in some manner or fly off into a vacuum forever.

It is not surprising to me that gasses respond to gravity and pool onto large planets. That is a form of containment. They have reached the escape velocity of each other but not the planetary escape velocity.

It is not surprising to me that heat, or at least hot and cold gases and liquids are effected by gravity. It's called natural convection. Try putting hot and cold blocks of copper together and see which way heat travels.


https://en.m.wikipedia.org/wiki/Escape_velocity

Google AI wrote:For a substance to exist as a gas, its molecules need to be moving at a speed where they can overcome the intermolecular forces holding them together, which typically requires an average molecular speed in the range of hundreds of meters per second depending on the substance and temperature involved; the exact speed depends on the molecule's mass and the temperature

The difference between liquid and gas is that the gas is free to travel, no longer bonded. Always has a pushing pressure. Expands to fill it's container.

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Fool wrote: ↑Sun Oct 06, 2024 9:43 am .

Tom Booth wrote:Many gases certainly do condense under pressure without cooling. You apparently don't know much about the history of the liquefaction of gases.

Liquefaction of gasses requires cooling. Propane, if compressed suffers from adiabatic temperature increase. It won't liquify if at a hotter temperature. It must be cooled, necessary to keep it at room temperature during compression.

https://m.youtube.com/watch?v=EaMfykiEYNc

Heat of compression prevents gas from liquefying by compression alone. Heat can be removed isothermally at room temperature, if compression is slow enough.

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Fool wrote: ↑Sun Oct 06, 2024 10:24 am .

Tim Booth wrote:Newton's Cradle, the actual device or demonstration model with the metal balls is far from the kinetic theory picture of gas molecules in random motion at high velocity. You elsewhere talk about "escape.velocity", so which is it?

The analogy of Newtons cradle breaks down when put in a vacuum. Go figure. Gases have greater than escape velocity and expand forever. Newtons cradle has leashes.

It is interesting to put a solid, liquid and gas, in a vacuum to see how the differ. Take water, ice and, steam.

The steam gets sucked away immediately and disappears down the vacuum hose to be exhausted outside.

The ice dries up by subliming directly from solid to vapor/steam. It gets colder.

The water starts boiling turning also into steam, but faster than ice. It gets colder. In fact it will keep getting colder even when ice starts forming in the boiling pool. Ice water and steam all from the same pool.

I suppose the question involved here regarding attraction and bonding would be how is it possible for all three to be bonded and only one, vapor/steam able to move by vacuum out of the chamber. Ice just sits there not showing any motion, just getting smaller. Water shows active boiling and freezing motion, but stays relatively pooled up. Somehow it just can't fully be attributed to locked-in-bonded-vibration. Water bonds move but don't let go. Vapor/steam very obviously let's go until bouncing off of something else, like a wall, or other molecule.

Since molecules of air are continuously bouncing off each other, a sound wave easily propagates through by producing a slightly modified coordinated group bounce effort, as it travels through in the direction of the sound wave before deciding back into the original random bouncing and moving.

Think about Brownian motion and how a bunch of collision can move a particle all around inside a stationary jar of liquid.

Solid is crystalline. Has a hold.

Liquid is in orbit. Juggling.

Gas is above the escape velocity. Watching them zip by and impacting, producing pressure always.



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Tom Booth wrote: ↑Sun Oct 06, 2024 12:36 pm
To put that into perspective, as per your reference, 68 nanometers is about 1500 times smaller than the average width of a human hair.

Relatively speaking I would consider that tightly packed and virtually unable to move at all without bumping into a neighboring gas molecules less than 1000th the width of a human hair away.

If you factor in that the gas molecules are held apart by the balance of attractive and repulsive molecular forces, are they actually moving, relative to one another, even the 1/1000th or less distance of a human hair?

How many human hairs do you need to stack up to reach from the hot plate to the piston in a Stirling engine?

Fool wrote: ↑Sun Oct 06, 2024 6:27 am
Gas has a separation, no longer bonded with free path and ability to escape. It must be contained in some manner or fly off into a vacuum forever.

It is not surprising to me that gasses respond to gravity and pool onto large planets. That is a form of containment. They have reached the escape velocity of each other but not the planetary escape velocity.

It is not surprising to me that heat, or at least hot and cold gases and liquids are effected by gravity. It's called natural convection. Try putting hot and cold blocks of copper together and see which way heat travels.

matt brown wrote: ↑Sun Oct 06, 2024 1:32 pm

Tom Booth wrote: ↑Sun Oct 06, 2024 12:36 pm
To put that into perspective, as per your reference, 68 nanometers is about 1500 times smaller than the average width of a human hair.

Relatively speaking I would consider that tightly packed and virtually unable to move at all without bumping into a neighboring gas molecules less than 1000th the width of a human hair away.

If you factor in that the gas molecules are held apart by the balance of attractive and repulsive molecular forces, are they actually moving, relative to one another, even the 1/1000th or less distance of a human hair?

How many human hairs do you need to stack up to reach from the hot plate to the piston in a Stirling engine?

Or...what is the density of a gas measured via (distance between molecules)/(size of molecules) ??? Hint...if 1 mole of gas in 1 cubic meter container had ALL the space between the molecules removed, you still couldn't see this mole in any corner of this container. What we call "air" is more vacuum than not...