I've been searching for several hours for the answer to a question. Maybe someone here can help.

When a substance undergoes a phase change from liquid to solid it releases a given amount of energy to its environment - i.e. Water releases about 333 kilajoules per kilogram when it turns into ice for example. We call this the enthalpy of fusion. Is this energy organized in a statistically predictable spectrum of photons? Is there a name for this spectrum/band of photons/quanta?

Any help is appreciated.

The heat can be conducted away, in which case I don't think there is an electromagnetic wave involved. But it can also be radiated away. In this case you need to use Wien's Displacement law.
Wavelength = 2.898 mm-Kelvin / Temp in Kelvins
= 2.898/273 = 10.6 microns
This is in the long wave infrared band.

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Bill Slugg
Albany, GA

I find that a rather strange way of putting it. If you remove the appropriate quantity of heat (ie, enough to get it to the freezing point temperature and the latent heat of freezing) and there is an adequate nucleation process, then it will freeze. The increased amount of heat was previously stored in the motion of the molecules jiggling around, which kept it liquid or gas, and can be taken away however you like. Take away enough heat and the atoms jiggle around less and stay put. The basics of a quantized type operation don't exist here. I don't think that another unfrozen molecule bonds itself to a solid state and a quantum of energy characteristic of the lower energy state of that molecule is radiated off into space. Think of what is happening in the reverse process. We don't have to ping a quantum of the right quantity to break that bond, rather it is conducted in.

Another way of understanding this is to realise that phase is a property that only makes sense if there is a sufficient quantity of matter. Whereas quantized processes typically depend upon transitions in single moelcules. A single molecule floating in space is necessarily in the gaseous state (if it retains its electrons). We can't ping it with a quantum and change its phase. It is still a gas, even if it is very cold.

Wien's displacement law is related simply to the temperature of the body. It has nothing to do with the quantity of energy per molecule or per bond being radiated from a phase change, nor the particular substance, nor its phase. Phase changes can happen at other temperatures, eg, the freezing of supercooled water in clouds.

It's definately a strange question. The general answer I'm getting is that there are other mechanisms besides photons which can remove the enthalpy of fusion - vibration and conduction. I'm sure these other mechanisms are the general heat transport modes but underneath this case there must be a radiant mechanisim.

Several replies I've gotten suggest the spectrum would be close to a black body spectrum. The only question I have is that there must be a difference between substances that change phase at the same temperature but have differing enthalpies.

I'm still searching.

I don't understand why a single particle floating in space is "necessarily in the gaseous state" - Hydrogen sure but not iron.

"Wien's displacement law is related simply to the temperature of the body. It has nothing to do with the quantity of energy per molecule or per bond being radiated from a phase change, nor the particular substance, nor its phase. Phase changes can happen at other temperatures, eg, the freezing of supercooled water in clouds."

I agree... freezing can also occur at what are traditionally considered superheated conditions.

I said molecule, not particle. "Particle" is ambiguous. It might mean something like a piece of sand, which is clearly solid.

A single molecule/atom floating in space is necessarily gaseous, because it is not bound to anything else, as it would be in a liquid or solid. Even if it is an iron atom.

I'm trying to point out that the energy level of a molecule does not necessarily affect what phase it is in. So pinging it with a quantum of energy, or getting it to release such a quantum, does not change its phase. Phase is not related to the internal energy of the molecule, but the energy of its motion and bonding. So this latent heat doesn't come in/out in quanta like the energy level of an excited molecule, where the electrons rise to higher or lower energy states in quanta. Rather the energy which makes the difference between phases is related to the bonding between the molecules/atoms, and diffuse across many such molecules/atoms. Moreover these are not the covalent bonds of well-defined energies of formation/breaking that exist within molecules. Phase changes are typically related to the motion/bonding energy of the atoms, not emission of photons. Though if you did persuade something to accept/release energy by a photonic process, that could drive a phase change, as with the sun shining on ice causing it to melt or sublime.

I'll have to take your word for it that a single CO molecule floating in space is gaseous depite the low temperatures. But then would two molecules make a solid? This doesn't make sense to me but it's off the issue.

While I am confused by your explanation I appreciate it. I would think bonding changes should be accompanied by quanta just as excitation is. Why wouldn't they?

Why is it that photons can be used to drive a phase change forward but photons don't come into play in the reverse direction? All vibration and conduction eh? I'm still puzzled but thanks for trying.

As was mentioned earlier, the released energy can escape as photons. In solids and liquids the energy levels get smeared out by the time the energy reaches the surface where it can escape into space. The familiar blackbody spectrum is explained by quantum mechanics, if I am not mistaken.

The other day I read an news article that talked about how a certain bacteria is the primary nucleator of ice and snow. Very Gaia-ish stuff... But then I thought when water freezes it releases a relatively substantial amount of energy so an organism that promoted freezing would do well if it was adapted to capitalize on some of the energy released when water freezes. This lead me to other thoughts.

My question became the subject of this thread which is what kind of energy is released in a phase change. I've gotten mixed replies but several individuals have suggested the wavelength of the energy released would be in the infrared. I was hoping for a slightly higher energy level but the top end of the infrared region is certainly capable of sustaining photosynthesis. The question then becomes could a photosynthetic autotroph use this energy? The closest known creature to this appears to be a photosynthetic bacteria that operates off the infrared light emitted by ocean vents. Today I wrote to one of the researchers in this area with my preliminary hypothetical science-fictionie idea.

The what if hypothesis is that there could be an organism that captures energy when water freezes. I've imagined that this organism's life cycle would consist of floating down to a certain depth in the ocean and capturing nutrients on the way... At a given depth it would initiate crystallization of water and capture some energy... This would be followed by a slow float up with the buoyant ice... During transit the organism could acquire various nutrients etc... Cycle repeat.

I realize this could seem preposterous. It's just a random mad scientist thought. Regardless of the merits of the idea I've learned a good deal during my little investigation. I've learned that "life" is much more diverse than I previously recognized. I was highly prejudice towards all life being indirectly solar. I knew about the sulfur vent critters but these seemed a frivolous exception to the rule. Well it turns out there are deep earth critters too - weird chemotrophic guys. The end result is that I've learned there are regions of habitability I never imagined.

Thanks to those who replied.