Given enough time in a sealed environment, can a cup of water change temperature

[Dilli]

If I remember right at 0 C, normal ATM, a cup of water in a closed system would reach an equilibrium of liquid, solid and gas states (I assume there is some space left for gas in the container?).

The "Over time, the collisions of molecules will pass energy between them, but this also introduces the possibility to nullify (not destroy) energy." - is the state change of water to gas / solid until equilibrium is reached. Though nullify is probably the wrong word to use, conversion of "heat" to "bonds between water molecules" (Hydrogen bonds?).

I am battling to remember my physics / chemistry, it has been too many years, so I may be wrong

Edited May 26, 2015 by Dilli
Checked the bonding of water molecules

[arkie87]

If I remember right at 0 C, normal ATM, a cup of water in a closed system would reach an equilibrium of liquid, solid and gas states (I assume there is some space left for gas in the container?).

The "Over time, the collisions of molecules will pass energy between them, but this also introduces the possibility to nullify (not destroy) energy." - is the state change of water to gas / solid until equilibrium is reached. Though nullify is probably the wrong word to use, conversion of "heat" to "bonds between water molecules" (Hydrogen bonds?).

I am battling to remember my physics / chemistry, it has been too many years, so I may be wrong

I dont think OP's question is at "normal ATM". Temperature is 0C and pressure is probably vapor pressure of water/ice at 0C. Otherwise, there is air in the system (and why would their be air in this system floating in space?). Regardless, it would make sense the air starts at 0C just like the rest of the system, in which case, the answer does not change.

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Is this chemistry or physics?

It is statistical thermodynamics... (which is both?)

[lajoswinkler]

If I remember right at 0 C, normal ATM, a cup of water in a closed system would reach an equilibrium of liquid, solid and gas states (I assume there is some space left for gas in the container?).

The "Over time, the collisions of molecules will pass energy between them, but this also introduces the possibility to nullify (not destroy) energy." - is the state change of water to gas / solid until equilibrium is reached. Though nullify is probably the wrong word to use, conversion of "heat" to "bonds between water molecules" (Hydrogen bonds?).

I am battling to remember my physics / chemistry, it has been too many years, so I may be wrong

No, it would not. Vapor is not gas. You're vaguely remembering triple point and you can't have air ("normal ATM") in your vessel for that.

For water to exist in a triple point you need to ensure 273.16 K and its partial pressure (also the total pressure in the vessel, as water is the only thing inside) needs to be 611.73 Pa. Then all of the three phases can coexist.

There is no nullification of energy in any case. Energy can not be destroyed in a thermodynamic system. If we ignore insane quantum phenomena that might occur during absolutely insane googol year experiments, and presume this is an isolated system with liquid water only, the water will remain liquid.

This thought experiment is lacking important detail, though. "A cup of water" - what does that mean? Water as in wet liquid thing or water as a compound? Is there anything else in the vessel, like atmosphere?

[Mr Shifty]

Who cares. But for science, because entropy always is increasing (therefore the heat of the object) it will liquefy after many, many, many, many, you get the idea, years.

Entropy does not equal heat. Maximum entropy for a macroscopic thermodynamic system just means that temperature is uniform throughout the system, so there's no gradient for heat transfer. And statistically all it means is that this is the most likely future state of the system. Entropy doesn't exist microscopically; it's just a statement that macroscopic systems are most likely to exist in states with a greater number of indistinguishable microscopic configurations.

[AngelLestat]

Yes, two molecules with opposite momentum might collide, perfectly cancelling out their momentum and energy. However, this is unlikely to occur, and, is unlikely to last a significant amount of time before other molecules bump into them, giving them non-zero momentum and energy. Laser cooling only works if it can selectively target molecules or otherwise bias the system in one direction.

2 cars in opposite directions crash, they both stop.. you mean that the energy of each car before the crash is gone now?

That would violate the thermodynamics laws.

Energy always transform in one way or another, so the opposite direction particles seems pointless.

[arkie87]

2 cars in opposite directions crash, they both stop.. you mean that the energy of each car before the crash is gone now?

That would violate the thermodynamics laws.

Energy always transform in one way or another, so the opposite direction particles seems pointless.

Yeah, good point. Molecular collisions are elastic, so both would bounce back with equal velocity. This mistake is mostly irrelevant to my point though.

[Skyler4856]

Temperature on a macroscopic scale is the average kinetic energy of every single atom in a substance.

Atom A has a kinetic energy of 1, Atom B has a kinetic energy of zero (Im aware that this isnt possible, just bare with me for sake of explantation). Both atoms collide, and cancel out. Both atoms have a new energy of 1/2, identical to that of the original average.

[Fel]

Yes, two molecules with opposite momentum might collide, perfectly cancelling out their momentum and energy. However, this is unlikely to occur, and, is unlikely to last a significant amount of time before other molecules bump into them, giving them non-zero momentum and energy. Laser cooling only works if it can selectively target molecules or otherwise bias the system in one direction.

Regardless of temperature, molecules follow a Boltzmann Distribution for their energies. Thus, even in thermal equilibrium, molecules are allowed to (and do) have different energies.

Thus, the only solution, is that the water remains at 0C (from the fact you called it water at 0C, i assume its in the liquid state at 0C), and due to the Boltzmann distribution, some ice/slush will form.

Boltzman is Newtonian, averaging a large substance overtime and under ideal conditions, but according to statistics, even a 0.01% event WILL happen with enough samples. This means the distribution is really saying what is most probable, but not what is physically limited to happening; i.e. if you pour a boiling cup of water into a "finely ground cup of subzero ice" you'll instantly violate the distribution even after the ice melts, until it comes to an equilibrium point. (And yes, I am aware that the definition states it is at thermal equilibrium, just was trying to explain that notion.)

The notion of "fallacy of infinite resonance" was suppose to explain that molecules traveling the same speed cannot transfer momentum in an additive way. Remember that resonance, in high school, is introduced as this magical thing and we have people talking about bringing down bridges or buildings with it. BUT even without internal losses, the speed of the hammer introduces a fixed limit on the energy output of the system. The system moves to PREDICT the hammer and hence when the system is moving at the speed of the hammer, you must increase the energy supplied to get more energy out.

Hence we get a problem that if two molecules hit and nullify, that to speed them back up it takes more supplied energy.

Of course, with the introduction of pressure high energy molecules can easily counter the low energy molecules and if we're considering that the bond-energy of the liquid may come into play when certain situations occur, what seemed like a simple issue likely faces more complex quantum issues that restrict it from occurring.

I've come to suspect that there may be more issues with isolation than I suspected. I wanted to say the system cannot lose or gain energy but if the walls of the glass get excited by molecular collisions then they too can release photons which hence can also excite molecules past the average temperature; this may act as a capacitive effect releasing more energy as the average kinetic energy decreases.

I'm also forgetting that ANY molecule can radiate energy at any given time... so long as the molecule isn't at absolute zero. This again places ways of bringing up the maximum molecular temperature (though it can also lower it). The problem that emerged was what was exciting the high-energy molecules.

I'm always surprised by people on these forums who never seemed to hear of the concept of "thought experiment", and would rather nit pick than be helpful.

If the water was held in an infinitely thin membrane (zero thermal mass), which was painted with a surface of emisivity = 0, then this thought experiment is valid in theory.

Of course, emisivity = 0 paint does not exist, but bothering to mention that would be missing the point.

It's rather ugg to me really, and that people are modifying how laser cooling works so that they don't have to think about vectorized energy (and hence negative energy) makes the point rather moot (you can't control or predict reemission). Statistically, we should be able to say that the net motion of the water is zero, but on the molecular level it is quite the opposite, hence vectors, associated energy levels, etc.

Take two DC electric motors, constructed of identical superconducting material and join them with a single non-conductive rod (I don't want to deal with flux, okay?) between them. Turn the system on and wait until equilibrium (basically some magnetic fields need to build up), after that the system will have zero losses. These are two motors, turning against each other... but no energy is being expended. No heat emitted, no losses (yes, assuming perfect containment). Do the systems have energy? Of course! Snap that rod and the motors will turn freely, so the systems have plenty of potential energy. Just that, a la superposition if it helps to have something to look up, the energies are nullified.

I hate to derail much, but it's a problem with my generation (or later even); anything outside of what we can look up online doesn't exist... and we don't even understand what we look up, nor look things up that contest with what we believe we know. People just don't bother challenging their own beliefs to come to radical new conclusions and when they believe they can supplement wisdom (knowing how to use the information) with intelligence (access to information) we get "this". I wrote this from a firm stance on the topics mentioned checked against non-internet sources to confirm the general conceptual issue and the responses basically told me to go back and check again.

Heck, since we were only talking about average kinetic energy (Temperature) the least people could do is say "okay, but the average potential energy in sum with the average kinetic energy remains the same"; bond energy seemingly being a good choice here as far as potential energy goes. (In theory, it takes large amounts of energy to push atoms closer together due to VSR, while water does undergo expansion due to crystallization, it will contract as temperatures decrease. Ergo the energy used to push the atoms together can also be released to push them apart / re-excite them. It may not be proportional, but it is energy.)

*yeah, this is really long*

Edited May 27, 2015 by Fel

[Fel]

Yeah, good point. Molecular collisions are elastic, so both would bounce back with equal velocity. This mistake is mostly irrelevant to my point though.

Newtonian simplification, if molecular collisions did not transfer partial momentums all elements would have thermal conductivity based solely on mass. The sum of all vectorized momentums needs be conserved, not the sum of all momentum magnitudes.

[DeepOdyssey]

If the walls don't absorb energy eg. purely elastic collision, and there's no heat exchange with outside system[perfectly isolated system] then the temperature will not drop. Even the "heat death" scenario for universe, wouldn't affect this container, as it is a perfect insulator.

[arkie87]

Newtonian simplification, if molecular collisions did not transfer partial momentums all elements would have thermal conductivity based solely on mass. The sum of all vectorized momentums needs be conserved, not the sum of all momentum magnitudes.

We were talking about a collision where the molecules are aiming directly at each other; thus, no vectorized momentums. Otherwise, obviously there are three momentum equations-- one for each dimension (any even angular momentum equations if there is rotation).

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Boltzman is Newtonian, averaging a large substance overtime and under ideal conditions, but according to statistics, even a 0.01% event WILL happen with enough samples. This means the distribution is really saying what is most probable, but not what is physically limited to happening; i.e. if you pour a boiling cup of water into a "finely ground cup of subzero ice" you'll instantly violate the distribution even after the ice melts, until it comes to an equilibrium point. (And yes, I am aware that the definition states it is at thermal equilibrium, just was trying to explain that notion.)

The notion of "fallacy of infinite resonance" was suppose to explain that molecules traveling the same speed cannot transfer momentum in an additive way. Remember that resonance, in high school, is introduced as this magical thing and we have people talking about bringing down bridges or buildings with it. BUT even without internal losses, the speed of the hammer introduces a fixed limit on the energy output of the system. The system moves to PREDICT the hammer and hence when the system is moving at the speed of the hammer, you must increase the energy supplied to get more energy out.

Hence we get a problem that if two molecules hit and nullify, that to speed them back up it takes more supplied energy.

Of course, with the introduction of pressure high energy molecules can easily counter the low energy molecules and if we're considering that the bond-energy of the liquid may come into play when certain situations occur, what seemed like a simple issue likely faces more complex quantum issues that restrict it from occurring.

I've come to suspect that there may be more issues with isolation than I suspected. I wanted to say the system cannot lose or gain energy but if the walls of the glass get excited by molecular collisions then they too can release photons which hence can also excite molecules past the average temperature; this may act as a capacitive effect releasing more energy as the average kinetic energy decreases.

I'm also forgetting that ANY molecule can radiate energy at any given time... so long as the molecule isn't at absolute zero. This again places ways of bringing up the maximum molecular temperature (though it can also lower it). The problem that emerged was what was exciting the high-energy molecules.

It's rather ugg to me really, and that people are modifying how laser cooling works so that they don't have to think about vectorized energy (and hence negative energy) makes the point rather moot (you can't control or predict reemission). Statistically, we should be able to say that the net motion of the water is zero, but on the molecular level it is quite the opposite, hence vectors, associated energy levels, etc.

Take two DC electric motors, constructed of identical superconducting material and join them with a single non-conductive rod (I don't want to deal with flux, okay?) between them. Turn the system on and wait until equilibrium (basically some magnetic fields need to build up), after that the system will have zero losses. These are two motors, turning against each other... but no energy is being expended. No heat emitted, no losses (yes, assuming perfect containment). Do the systems have energy? Of course! Snap that rod and the motors will turn freely, so the systems have plenty of potential energy. Just that, a la superposition if it helps to have something to look up, the energies are nullified.

I hate to derail much, but it's a problem with my generation (or later even); anything outside of what we can look up online doesn't exist... and we don't even understand what we look up, nor look things up that contest with what we believe we know. People just don't bother challenging their own beliefs to come to radical new conclusions and when they believe they can supplement wisdom (knowing how to use the information) with intelligence (access to information) we get "this". I wrote this from a firm stance on the topics mentioned checked against non-internet sources to confirm the general conceptual issue and the responses basically told me to go back and check again.

Heck, since we were only talking about average kinetic energy (Temperature) the least people could do is say "okay, but the average potential energy in sum with the average kinetic energy remains the same"; bond energy seemingly being a good choice here as far as potential energy goes. (In theory, it takes large amounts of energy to push atoms closer together due to VSR, while water does undergo expansion due to crystallization, it will contract as temperatures decrease. Ergo the energy used to push the atoms together can also be released to push them apart / re-excite them. It may not be proportional, but it is energy.)

*yeah, this is really long*

If you understand all this, then what is your question: you know that ice formation is allowed and possible from a statistical thermodynamics perspective (though unlikely to form a "slushy" consistency)?

[ZetaX]

Hence we get a problem that if two molecules hit and nullify, that to speed them back up it takes more supplied energy.

Such a long response and that line, yet you still have not responded to the quite obvious fact that your "process" is violating thermodynamics (especially conservation of energy). All you do is calling it "nullify" and then acting like that is an accepted concept in physics; it is not, it is pure quackery.

[arkie87]

Such a long response and that line, yet you still have not responded to the quite obvious fact that your "process" is violating thermodynamics (especially conservation of energy). All you do is calling it "nullify" and then acting like that is an accepted concept in physics; it is not, it is pure quackery.

Maybe that is OP's problem. OP thinks two colliding particles with equal but opposite momentum will impact and stop moving. Over time, this would lead to cooling down of the system. However, as numerous people have stated, molecular collisions do not occur in this way. Two colliding particles with equal but opposite momentum will bounce back from each other with equal but opposite velocities (assuming the particles have equal mass). Momentum and energy must be conserved; and if both particles has zero velocity, energy would be destroyed.

Edited May 27, 2015 by arkie87

[lajoswinkler]

You forgot about photons, too. If the system has chaos, the matter inside will radiate low energy photons and if the system is isolated, they will continuously reflect into the matter and keep it at the same temperature. Even if the particle collisions were perfectly non-elastic, joined particles would emit a photon.

If the system was just closed in a zero kelvin universe, photons would carry away the heat and, gradually, the matter inside would cool down until it has zero point energy. In our universe away from any clump of matter such as a star or a planetary body, it would cool down to the background temperature as it gets into thermal radiative equilibrium.

[arkie87]

You forgot about photons, too. If the system has chaos, the matter inside will radiate low energy photons and if the system is isolated, they will continuously reflect into the matter and keep it at the same temperature. Even if the particle collisions were perfectly non-elastic, joined particles would emit a photon.

If the system was just closed in a zero kelvin universe, photons would carry away the heat and, gradually, the matter inside would cool down until it has zero point energy. In our universe away from any clump of matter such as a star or a planetary body, it would cool down to the background temperature as it gets into thermal radiative equilibrium.

Clearly, it needs to be enclosed in a zero emisivity membrane.

[KSK]

Maybe that is OP's problem. OP thinks two colliding particles with equal but opposite momentum will impact and stop moving. Over time, this would lead to cooling down of the system. However, as numerous people have stated, molecular collisions do not occur in this way. Two colliding particles with equal but opposite momentum will bounce back from each other with equal but opposite velocities (assuming the particles have equal mass). Momentum and energy must be conserved; and if both particles has zero velocity, energy would be destroyed.

Kinetic energy would be destroyed but it's entirely possible for that kinetic energy to be converted into another form. A particle accelerator is the most extreme example of this where, very loosely speaking, the particles collide at equal and opposite velocities and turn into a tiny fireball which then cools down to create a bunch of new particles. E=mc2, the kinetic energy of the colliding particles is converted to mass.

In a less extreme, everyday example, the particles collide at the right orientation, and with sufficient energy to overcome an activation barrier and merge to form a new particle. Bits of that larger particle may fly off in the process. Kinetic energy is converted to energy locked up in new chemical bonds and/or kinetic energy of the bits that flew off. In other words, a chemical reaction happens.

Edited May 28, 2015 by KSK

[arkie87]

Kinetic energy would be destroyed but it's entirely possible for that kinetic energy to be converted into another form. A particle accelerator is the most extreme example of this where, very loosely speaking, the particles collide at equal and opposite velocities and turn into a tiny fireball which then cools down to create a bunch of new particles. E=mc2, the kinetic energy of the colliding particles is converted to mass.

In a less extreme, everyday example, the particles collide at the right orientation, and with sufficient energy to overcome an activation barrier and merge to form a new particle. Bits of that larger particle may fly off in the process. Kinetic energy is converted to energy locked up in new chemical bonds and/or kinetic energy of the bits that flew off. In other words, a chemical reaction happens.

Both of those examples are not applicable to this discussion. Clearly, (following the spirit of the OP), there is no fusion or chemical reactions.

[KSK]

Both of those examples are not applicable to this discussion. Clearly, (following the spirit of the OP), there is no fusion or chemical reactions.

Of course. But it still makes the point that the second part of the statement "Momentum and energy must be conserved; and if both particles has zero velocity, energy would be destroyed." is wrong. Zero velocity does not mean that energy has been destroyed, only that kinetic energy has been converted to some other form.

[arkie87]

Of course. But it still makes the point that the second part of the statement "Momentum and energy must be conserved; and if both particles has zero velocity, energy would be destroyed." is wrong. Zero velocity does not mean that energy has been destroyed, only that kinetic energy has been converted to some other form.

Uggh.... really?

Clearly, that statement was applying only to the discussion at hand, and not a sweeping statement.

In this particular example, if two colliding particles of equal masses impacted and had zero velocity afterwards, it would be destroying energy, so it's not possible. Or are you saying that its possible (and by possible, i mean likely)?

If not, i dont understand what you are adding to this discussion, other than quoting a very contextual statement of mine out of context

[KSK]

Uggh.... really?

Clearly, that statement was applying only to the discussion at hand, and not a sweeping statement.

In this particular example, if two colliding particles of equal masses impacted and had zero velocity afterwards, it would be destroying energy, so it's not possible. Or are you saying that its possible (and by possible, i mean likely)?

If not, i dont understand what you are adding to this discussion, other than quoting a very contextual statement of mine out of context

First of all, lets agree to ditch this nonsense about destroying energy (and yes, I carelessly used that phrase myself - sorry). Energy can't be destroyed, merely converted from one form to another.

In this particular example, we're talking about a cup of water and yes, in principle, two water molecules can collide and have zero velocity afterwards. Please note that they won't have come to a complete halt - you'll still have bond vibrations - but add up the velocity vectors of all six atoms in those two molecules and the total will be zero. The kinetic energy of both molecules before the collision has been converted to a new chemical bond (in this case a hydrogen bond), which will have kinetic and potential energy associated with it - think two balls connected by a spring, and any excess energy will be radiated away.

Granted, for this to happen, the two molecules have to be moving pretty slowly but that's OK because in this example, we're assuming that the water is at zero degrees, so for a reasonable range of pressures it's going to be at it's freezing point, which is exactly the point at which the molecules will start sticking together as described above.

More generally, if it wasn't possible for particles to impact and have zero net velocity afterwards, then nothing would ever be able to freeze. Those particles won't necessarily have equal mass - think nucleation, where a tiny ice crystal grows, essentially by having water molecules stick to it - but the idea is the same in each case - particles collide, momentum is conserved, kinetic energy is converted to chemical bond, excess energy radiates away.

[arkie87]

First of all, lets agree to ditch this nonsense about destroying energy (and yes, I carelessly used that phrase myself - sorry). Energy can't be destroyed, merely converted from one form to another.

In this particular example, we're talking about a cup of water and yes, in principle, two water molecules can collide and have zero velocity afterwards. Please note that they won't have come to a complete halt - you'll still have bond vibrations - but add up the velocity vectors of all six atoms in those two molecules and the total will be zero. The kinetic energy of both molecules before the collision has been converted to a new chemical bond (in this case a hydrogen bond), which will have kinetic and potential energy associated with it - think two balls connected by a spring, and any excess energy will be radiated away.

Granted, for this to happen, the two molecules have to be moving pretty slowly but that's OK because in this example, we're assuming that the water is at zero degrees, so for a reasonable range of pressures it's going to be at it's freezing point, which is exactly the point at which the molecules will start sticking together as described above.

More generally, if it wasn't possible for particles to impact and have zero net velocity afterwards, then nothing would ever be able to freeze. Those particles won't necessarily have equal mass - think nucleation, where a tiny ice crystal grows, essentially by having water molecules stick to it - but the idea is the same in each case - particles collide, momentum is conserved, kinetic energy is converted to chemical bond, excess energy radiates away.

Destroying energy was mentioned to indicate that what was mentioned previously is not possible. I dont understand your fear of this phrase (much like some mathematicians fear of dividing by zero).

Yes, for materials with atomic structures more complicated than a single-atom ideal gas, it is possible to have collisions resulting in zero velocity, with the kintetic energy being converted into some other form of energy. Since water is a liquid, there are hydrogen bonds (and if it happens to freeze into ice, then crystal bonds), so, in that light, it is possible to have a collision resulting in zero (or near zero) velocity.

Though i dont think it is a requirement to have collisions resulting in zero velocity for freezing to occur. Velocity just must be below some threshold to keep its kinetic energy below the energy threshold of the bond's energy well. Even molecules in a solid do poses kinetic energy, and it is quid significant, especially near freezing point.

[KSK]

Agree with all of that, although I'm not sure (honest question, not a snark) what you mean by crystal bonds in ice?

Edit - this is why I used the term 'net velocity'. Not sure how correct it is technically, but I was trying to cover bond vibrations, where the vibrating particles spend half their time going one way and half their time going the other way - hence zero velocity on average.

I don't like the term 'destroying energy' partly because it's just wrong and looks ridiculous in a supposedly scientific discussion thread, but mostly because it leads to unhelpful arguments where it's not clear if the poster is using 'destroys energy' as a synonym for 'energy is not conserved' or whether there's a genuine misunderstanding at play.

Take. "In this particular example, if two colliding particles of equal masses impacted and had zero velocity afterwards, it would be destroying energy, so it's not possible."

Whatever interpretation you put on 'destroying energy' that statement is incorrect.

Anyway, we seem to agree on the main points so I'll stop here.

Edited May 29, 2015 by KSK

[arkie87]

Agree with all of that, although I'm not sure (honest question, not a snark) what you mean by crystal bonds in ice?

Edit - this is why I used the term 'net velocity'. Not sure how correct it is technically, but I was trying to cover bond vibrations, where the vibrating particles spend half their time going one way and half their time going the other way - hence zero velocity on average.

I don't like the term 'destroying energy' partly because it's just wrong and looks ridiculous in a supposedly scientific discussion thread, but mostly because it leads to unhelpful arguments where it's not clear if the poster is using 'destroys energy' as a synonym for 'energy is not conserved' or whether there's a genuine misunderstanding at play.

Take. "In this particular example, if two colliding particles of equal masses impacted and had zero velocity afterwards, it would be destroying energy, so it's not possible."

Whatever interpretation you put on 'destroying energy' that statement is incorrect.

Anyway, we seem to agree on the main points so I'll stop here.

As i intended it, I think "destroys energy" and "energy is not conserved" are functionally the same thing, though i see your point that if you dont know the intent of the speaker, "destroys energy" might indicate the speaker believes energy can be destroyed.

I think its particularly important to observe context: "it would be destroying energy, so it's not possible" should indicate that i understand destroying energy is not possible, and meant it as "energy is not conserved". They are functionally the same thing, but i prefer to explain all things without jargon (especially on a forum where non-experts might traverse).

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Agree with all of that, although I'm not sure (honest question, not a snark) what you mean by crystal bonds in ice?

Edit - this is why I used the term 'net velocity'. Not sure how correct it is technically, but I was trying to cover bond vibrations, where the vibrating particles spend half their time going one way and half their time going the other way - hence zero velocity on average.

I don't like the term 'destroying energy' partly because it's just wrong and looks ridiculous in a supposedly scientific discussion thread, but mostly because it leads to unhelpful arguments where it's not clear if the poster is using 'destroys energy' as a synonym for 'energy is not conserved' or whether there's a genuine misunderstanding at play.

Take. "In this particular example, if two colliding particles of equal masses impacted and had zero velocity afterwards, it would be destroying energy, so it's not possible."

Whatever interpretation you put on 'destroying energy' that statement is incorrect.

Anyway, we seem to agree on the main points so I'll stop here.

Crystal bonds = lattice vibrations. I had a brain fart and could not think of the word.

It might have zero velocity on average, but that is irrelevant since liquids might have zero velocity on average if you conisder a long enough period of time. Obviously, solids and liquids have kinetic energy so RMS is a better measurement than average velocity.

[KSK]

Crystal bonds = lattice vibrations. I had a brain fart and could not think of the word.

It might have zero velocity on average, but that is irrelevant since liquids might have zero velocity on average if you conisder a long enough period of time. Obviously, solids and liquids have kinetic energy so RMS is a better measurement than average velocity.

Gotcha - thanks. I'm used to thinking of hydrogen-bonded structures in a geometric sense (my PhD was on designing hydrogen-bonded structures starting from small organic molecules), so my first thought was 'the hydrogen bonds are the crystal bonds' but I figured you'd know that anyway.

And yes - RMS is a better measurement - good point.