In a physics, spherical cow universe, say you have a chamber being kept at exactly 0 degrees C at exactly one atmosphere. What would happen if you put in a glass of water? How about a cube of ice?
Would the water stay water? The ice stay ice? Or, would you end up with a slurry of ice and water either way?
I think it’s door number three is the right answer, but others here disagree.
Also, Happy Thanksgiving!
If the chamber is “kept at exactly 0 C” by virtue of just being really well-insulated, then the water would stay as it is. You need to add heat to melt ice, or remove heat to freeze water, and that heat has to come from or go to somewhere.
If the chamber is kept at that temperature by means of some active refrigeration system with a thermostat, then it would be possible for it to go either way. But depending on how the thermostat system is set up, you probably wouldn’t reach an equilibrium with some ice and some liquid. Most likely, you’d either end up stable at all liquid, stable at all solid, or oscillating between the two.
Can you elaborate on just what “a physics, spherical cow universe” is?
ETA: OK, wiki explained that to me. Spherical cow - Wikipedia
I’m sorry there’s no strong correlation with Gary Larson.
“assume ideal conditions which are not realistic in practice”
Which is why I failed physics. I couldn’t relate these things to real world experience.
as always, there’s an XKCD For that.
I’m probably not thinking clearly because of the turkey overload, but if it were oscillating, wouldn’t that imply that it’s always a slurry, except for the occasional extremes?
Here’s a link to the web page for that. You get the hover text plus an excuse to catch up on the latest comics while you’re there.
As described in t the OP, the answer would be “it depends”. Phase changes are an example of places where things change drastically from one side to the other.
For real world, Mr Faraday did something similar in his Christmas lectures (I think I found on Gutenberg). I think it was “fill metal can with water, put it into ice water bath, can explodes at just below freezing point as it solidifies “
There’s also the “put steam in can or bottle, quick cool, see the can implode when the steam condenses.
I prefer spherical pigs vs cows. Physically perfect bacon.
Happy thanksgiving to you too.
Hope your spherical cow universe extends to Chemistry too.
If so, 100% pure water (even fairly pure water ) will not freeze but get supercooled until about -40C. Water needs nucleation sites to freeze.
Also the melting point of ice is like 0.002 C, so it too will remain frozen because the temperature in this perfect universe is perfectly 0 C.
This is an interesting question because the chamber is kept at precisely 0º. I think the thermostat aspects of how that’s done need to be ignored for “spherical cow” reasons. Point being, the temperature is kept constant. Instead perhaps think about putting water/ice outside some place that’s exactly 0º so no matter what the water/ice does, it doesn’t affect the temperature of its surroundings.
Anyway, my first thought is that it would stay in the state it was put into the chamber. So if you put water in, it stays water, if put ice in, it stays ice. I don’t have much to back that up, but I guess the question is can the latent heat be released/absorbed when the chamber is kept at 0º? I don’t think it can. It seems there’s a thermal “nudge” factor that’s necessary to start the freezing/melting process. So at 0.0000…1º the ice would start to melt, or at -0.0000…1º the water would start to freeze, but at exactly 0º no phase change happens.
At 0.00001º C, the melting has already completely finished. The temperature won’t budge above 0 until all the melting is done.
I think your thought experiment should say the chamber walls are perfectly adiabatic so we can forget quibbling about what exact temperature you should specify.
The ratio of ice, water, water vapor and air should stay pretty nearly the same. But there are energy differences inside your chamber because of the geometry of the interfaces and the interfacial surface energies therein. All of the interfaces are going to include all of the phases and chemical species diffusing back and forth, though if the local energies in the system aren’t changing, the diffusion rates are the same in each direction.
I think the local energies are going to change for a while to dissipate locally higher interfacial tension energies. For example, if there are any sharp corners on the ice, they will round themselves off, and ice will grow elsewhere on the block. I also think anyplace there are separate blobs of any species, these will coalesce. All of this will minimize the surface energies. As that process exponentially decays over the thousands, millions, and billions of years, the system will stop evolving.
While it’s true that the system will evolve in that way, I’m skeptical that any of the processes would have timescales as long as thousands of years. I mean, in an open system, ice can sublimate away entire over the course of days or weeks.
I thought that the triple point of water was 0.01°C. Surely, at 0°C, the ice would remain as ice. Perhaps, over time, the interaction between negatively charged oxygen and positive hydrogens might, as Napier says above, cause ‘rounding’ of corners until the ice settled into a perfect sphere (assuming no gravity)
It will freeze. Because the melting point of pure water is not 0 °C. 
The last time NIST measured it (in 1995), they determined the melting point of pure water is 0.000089 °C ± 0.000010 °C.
It is. But it doesn’t have anything to do with the melting point of water. The triple point of water can only occur when the pressure is 611.657 pascals, which is less than 1% of standard atmospheric pressure.
A triple point is specified by temp and pressure. Well, partial pressure which isn’t all that easy to get your head around if you haven’t studied this. In the case of water it is 0.00603659 atm. So conditions have to be juuuust a bit right.
Yeah, but in an open system the driving potential is most of the vapor pressure of water at those conditions. In the OP’s closed system the driving potential is a very tiny fraction of that, especially in the limit as the sharpest curvatures round themselves off.
On another note, the OP doesn’t say whether the chamber has exclusively water in it, or was there air in there too? That is, is this a special chamber where we pump a hard vacuum before introducing the water and ice, and were they purified so as not to have dissolved air in them?
Note the ice point and the triple point are two (slightly) different temperatures.
If you pump a hard vacuum, then we’d have to change the temperature. I do specify that it’s exactly at one atmosphere.
Crafter_Man, good catch, but let’s assume that the chamber is exactly at the freezing/melting point of water at whatever the exact pressure is.
Napier, I’m not quite sure what you’re saying. Does the end point matter whether you start with a cup of water or a cup of ice? If you started with a slurry that’s already at 0 degrees C (+/- the Crafter_Man factor)?