I have grown up believing that water freezes at 32F (0C). I seem to see alot of references about 32F being the melting point of ice. If I take a glass of water and a glass of ice into a room that is 32 degrees what will happen to the 2 glasses over time? Will the ice melt or will the water freeze? I’m sure there is a simple answer.
Please go easy on the :smack: and :wally
Water begins to freeze at 4 degrees Celsius. IIRC it’s hard frozen at 0 degrees Celsius. So, the ice would not melt, but the water would freeze.
Freezing is not an instantaneous process. If my calculations are correct, water begins freezing at about 39 degrees F and is hard frozen at 32.
I am sorry but there is no way that water is going to begin to freeze at 39 F (whatever that means). You can leave water at that temperature forever and it is just really cold water. That’s it.
Water can exist as a solid (ice), liquid (water), and vapor (vapor 
) all at 32f. The diference in states is the latent heat of vaporization and latent heat of fusion. If you take a block of ice, and start pumping heat into it, for a while, it doesn’t change temperature. It melts, leaving you with some water and some ice, all at the same temperature. If you keep on pumping heat into it, more ice melts, and some of the water vaporizes, still all at 32f.
Clarification: The initial block of ice would have to be uniformly 32f for the above post to be true. If the ice is below 32f, if will change temperature until it reaches 32f, where it starts melting.
Also, ice is not a superconductor of heat energy, so one side of your block could quite easily be 32f while the other side is some much colder tmperature.
Also, see here for some relevant discussion.
Surely water will freeze at above ambient temps of 0C due to cooling by evapouration?
I can’t believe some of the misinformation already posted in this thread. If you take ice and start adding heat uniformly, the ice will increase in temperature at the rate of 1C per calorie per CC. When it reaches 0C it will begin to melt and continue to absorb heat at the rate of (IIRC) 80calories per gram. At 0C both water and ice coexist until all the ice has melted. The amount of heat supllied at each moment determines how much ice has melted. Once all the ice has melted the temperature of the water will rise at the rate of 1C per calorie per gram. If you stop supllying heat when half of the water is liquid and the other half solid, then nothing happens and it remains like that. What did you expect?
How can anyone say that there is no way that water is going to begin to freeze at 39 degrees if he doesn’t know what begins to freeze means?
This website explains what happens to water at 39 degrees. I believe “begins to freeze” is a fair characterisation of what is happening and I have heard it referred to as such in many science classes.
Certainly, if the water never gets below 39 degrees it won’t freeze, but then I don’t believe that was what I implied, either.
Well, if “freeze” means “turn from liquid to solid”, then water doesn’t begin to freeze until it hits 32F. Sure, it starts CHANGING before it reaches 32F, but it remains liquid while it’s changing.
Actually, water won’t freeze even at 32F unless it has a seed crystal to grow upon. Microscopic ice crystals melt (grow smaller) at 32F, so if a nano-crystal should spontaneously form, it will instantly melt again. For this reason you can chill water to well below 32F, then drop a seed crystal into the “supercooled” water and the tiny crystal will enlarge like mad.
A classic trick is to chill some cola or beer to below 32F in the freezer, then pop the cap. As the carbonation bubbles appear, they trigger the formation of fairly large ice crystals: when you remove the cap, the supercooled water instantly turns into slush.
How would a nano-crystal suddenly “spontaneously form”?
I guess the answer SQUID is looking for is that the glass of water would remain liquid and the ice would remain frozen. Right? Unless there are some of those nano-crystals lurking about.
Unfortunately, Sailor is right, there is a lot of hooey concocted out of thin air that some people are passing off as fact on this board. Water and ice are in equilibrium at 32F, nothing will happen in a closed system. If heat is added, more ice will melt, and vice versa. The assertion that water begins to freeze at 39F or some other temperature is the ramblings of a scientific illiterate. I think this person heard at some point that water’s density peaks at 39F and has mixed up facts to suit his concoction.
No-ones answered my question yet, wouldn’t water start to freeze at above ambient temps of 0C due to evapouration.
Water and ice co-exist at 32F or 0C. In a closed system, the ice won’t melt and the water won’t freeze. They’ll both just stay at 0C.
Sailor: if one adds one calorie of heat to a CC of ice, then it will increase by more than 1 degree Celcius for two reasons: (A) it takes less heat to warm ice by 1 degree than it does to warm an equivalent mass of water, and (b) 1CC of ice is less mass than 1cc of water.
Tranquilis: Water and ice co-exist at 0C at normal pressure; the triple point of water (where water, ice, and vapor co-exist) is just above 0 C (but not by much) when the vapor pressure is low.
No. Water COOLS because of evaporation, and when it cools to 32?F it will freeze. The only way this is going to happen is by air movement, which is why they call it “wind chill.”
Yes, but water cools easily by conduction as well and I’m pretty sure that evapouration still takes place (obviously at a much reduced rate) without wind chill. So I’m led to think that even when the ambient temp is above 0 C water will be slightly cooler than it’s surroundings.
I should of added to the last sentence “which could possibly lead to the formation of ice crystals”
Also, I should of said that I KNOW evapouration doesn’t need air movement for it to work.
This problem has always interested me from a Calculus point of view. The specific heat of water (and many other substances) is discontinous at any phase change (solid-liquid, liquid-solid). The specific heat at any phase change is undefined (or is infinite depends on how you look at it).
Let me explain it like this. Take two cases both dealing with say 80g of water (easier in CGS Units) :
Case I - Say the water is at 10deg C and you add 80cal of heat. The temperature of the water will increase by 1 deg. Or say you removed 80cal of heat, the temperature will be reduced to 9 deg C.
Case II - Say the same water is now at the freezing point (0 deg. C) and you added 80 cal of heat, the temperature increases to 1 deg C. But now, if you removed 80 cal of heat, temperature of water does’nt fall by 1 deg, Instead 1 g of ice will form. So if you are looking from a mathematician’s point of view, this is an doscontuinity (or the specific heat is infinity).
Another thing to remember, is that the maximum density of water is at 4 deg C. Water and Ice below this temperature will be lighter as well as the Water above this temperature. This is very important because it lets organisms live at the bottom of frozen lakes. Of course the low thermal conductivity of water is also important.
:eek:
If you continue to add heat (latent heat of fusion) it will continue to melt until it is in a completely liquid state. Additional heat will raise the temperature (sensible heat) until the liquid reaches 212f (100c), add additional heat (latent heat of vaporisation) and the water will begin to vaporize, assuming we are at sea level.
From my searching I understand that water can exist in all three states in the atmosphere at once. I have to disagree, however, that from a single block of ice you can generate steam at 32f (0c), while the ice still exists.
Evaporation may occur but that has more to do with air currents than heat.
I am not a physicist so I fully admit I may be incorrect. Please enlighten me in that case 
.
Grit - your post reflects some of the very widely accepted approximations which are as usual not quite correct. Let me start explaining
Vapor Pressure: Think of the water body as containing molecules just like the kinetic theory of gases. These molecules will continue to hit the surface of the water (remember the temperature is an macroscopic average quantity - so there are some highly energetic molecules at whatever temperature you are at) and escape the surface. Now, if you cover the space above the water, these molecules go into the air above the water until the partial pressure of the water molecules in the space above (mostly partial pressure of the water vapor = volume fraction of water vapor in the air above times the total pressure of te air) becomes equal to the vapor pressure of the liquid at that temperature.
At this pressure the amount of molecules vaporizing from the water to the air is the same as the vapor condensing back from the air to the water. Its a dynamic equilibrium. Now if you reduce the pressure above the water, more water vapor will escape the water to the air to maintain the partial pressure equal to the vapor pressure.
Evaporation as you normally understand occurs when you never let the water to achieve the above equilibrium. So that means if you keep blowing air over the surface of the water, water keeps giving off more and more vapor to achieve the vapor pressure but it never does because you remove the water vapors coming out.
The block of ice is not making steam, its just giving off molecules at its surface due to the velocity of the molecules also this is nothing compared to that water does.
The triple point of many materials is described as the point all the phases (S/L/G) coexist in dynamic equilibrium. At this point water gets converted to ice/vapor and vice versa. In fact all phases are converting to each other but the net change is ZERO.
Triple point is more accurately determined than boiling point or freezing point and is often used to characterize compounds.