stinsonbr
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Can someone explain how this happens?
I am not sure, if that would be a part of the answer then please explain it.DrClaude said:What is the temperature of the ice?
Yes and no...stinsonbr said:I had read that it had something to do with the process of ice melting making the ice itself colder?
Heat is given up by the solid phase (ice) in the process of dissolving/diluting alcohol.Bystander said:Google "freezing point depression."
Actually, that isn't true(you aren't the only one who said it...): they meet at the freezing temperature of the liquid, regardless of either's starting temperature.Ibix said:The ice cools the drink; the drink warms the ice. The will meet at a temperature in the middle somewhere.
This is exactly what I was trying to fish out. Can you give an "explain like I'm five" explanation on how this happens?russ_watters said:Actually, that isn't true(you aren't the only one who said it...): they meet at the freezing temperature of the liquid, regardless of either's starting temperature.
So that means, counter-intuitively, that they can end up colder than either started.
So the only thing that matters here is the freezing temp of the drink (as long as you add enough ice to reach it).
Not necessarily. Put a cube of ice from the freezer in liquid nitrogen. Do you expect the nitrogen to freeze?russ_watters said:Actually, that isn't true(you aren't the only one who said it...): they meet at the freezing temperature of the liquid, regardless of either's starting temperature.
That can happen below 0, if the ice starts cold enough.NihalRi said:As soon as the ice and alcohol reach the same temperature the heat exchange will stop.
A five year-old doesn't have much chance here, but I'll try to be basic...stinsonbr said:This is exactly what I was trying to fish out. Can you give an "explain like I'm five" explanation on how this happens?
No, that isn't what I said and is a totally different and much simpler situation because the nitrogen is boiling, not freezing and the temperature is lower, not higher than the ice temp.mfb said:Not necessarily. Put a cube of ice from the freezer in liquid nitrogen. Do you expect the nitrogen to freeze?
Iàm sorry, but I donàt see how that can be a general statement. What assumptions are you making here?russ_watters said:Actually, that isn't true(you aren't the only one who said it...): they meet at the freezing temperature of the liquid, regardless of either's starting temperature.
I'm pretty sure both of those are impossible (unstable). Could you please detail the conditions that could cause them?mfb said:It is an interesting situation if the two phases are not the same material. We can have several different options, if we neglect mixing of the substances:
If the freezing point of the liquid is below the freezing point of the solid:
...
- nothing melts, nothing freezes, the final temperature is between the freezing/melting points
- nothing freezes, something melts, the final temperature is at the melting point of the solid
If you have solid steel and liquid water, the steel stays solid and the water stays liquid. Nothing freezes. Nothing melts.russ_watters said:I'm pretty sure both of those are impossible (unstable). Could you please detail the conditions that could cause them?
This thread is about a water/alcohol mixture (perhaps also with sugar) in ice. If there are more complicated/different situations that have different outcomes, I don't thing it is wise to muddle the thread with them, particularly when the OP specifically asked for simplicity.DrClaude said:Iàm sorry, but I donàt see how that can be a general statement. What assumptions are you making here?
Even then, I don't see why you say temperature is not a factor. If the initial temperature of the ice is low enough, you can end up with the liquid freezing completely and the final mixture ending up below the freezing point of the liquid.russ_watters said:This thread is about a water/alcohol mixture (perhaps also with sugar) in ice. If there are more complicated/different situations that have different outcomes, I don't thing it is wise to muddle the thread with them, particularly when the OP specifically asked for simplicity.
Jeez, seriously!Bystander said:No one's made ice cream?!
Only if you have a really bad bartender.DrClaude said:Even then, I don't see why you say temperature is not a factor. If the initial temperature of the ice is low enough, you can end up with the liquid freezing completely and the final mixture ending up below the freezing point of the liquid.
Ok, fair enough. And that's assumptions/a situation far outside the scope of the OP's question. I submit that by expanding the issue so much before he has an understanding of the situation he's asking about (particularly when simplicity was requested), that makes reaching an understanding of that situation less likely.jbriggs444 said:If you have solid steel and liquid water, the steel stays solid and the water stays liquid. Nothing freezes. Nothing melts.
The steel/water example is just an extreme one, the ice/drink setup has the same properties. If ice and drink are at -2C for example, they are in thermal equilibrium (by definition of temperatures). Nothing melts or freezes, assuming the alcohol content is sufficient.russ_watters said:Ok, fair enough. And that's assumptions/a situation far outside the scope of the OP's question. I submit that by expanding the issue so much before he has an understanding of the situation he's asking about (particularly when simplicity was requested), that makes reaching an understanding of that situation less likely.
Agreed, and in the real world that can happen since sometimes people keep their alcohol in the same freezer as their ice. The wording of the question in the title implies that isn't the starting condition.mfb said:If ice and drink are at -2C for example, they are in thermal equilibrium (by definition of temperatures). Nothing melts or freezes, assuming the alcohol content is sufficient.
Correct.ToddSformo said:How about this: freezing is exothermic reaction, latent heat is given off. Melting is an endothermic reaction. So when ice is added to alcohol, it takes energy to melt the ice, and the energy comes from the liquid, in the form of heat, which, in turn, lowers the temperature of the ice-alcohol system?
If both start below zero, yes.mfb said:If the temperature is below zero, no melting happens.
That remains the main issue of the thread and it is not correct.You cannot reach an equilibrium temperature below zero if ice melts (neglecting transient effects from finite heat conductivity and so on)
Only if you take things like cooling from mixing into account, and even then I did not see a convincing situation yet that would prove this. If you do not (e.g. separate ice and drink by a thin plastic sheet), this is not possible. Heat will flow from the warmer to the colder object, heating the colder object.russ_watters said:Keeping within the narrow question, the interesting/difficult/counterintuitive behavior is that both the ice and drink can cool down when you combine them if both start above the freezing point of the drink.
I'm not certain what you mean by "cooling from mixing", but yes, if you wrap the ice in plastic it will not be able to go into solution with the drink when it melts, producing different results. For example, if the ice starts at 0C and the drink above 0C, it will have an equilibrium at 0C (assuming sufficient ice).mfb said:Only if you take things like cooling from mixing into account, and even then I did not see a convincing situation yet that would prove this. If you do not (e.g. separate ice and drink by a thin plastic sheet), this is not possible. Heat will flow from the warmer to the colder object, heating the colder object.
russ_watters said:I'm not certain what you mean by "cooling from mixing"
russ_watters said:but yes, if you wrap the ice in plastic it will not be able to go into solution with the drink when it melts, producing different results.
russ_watters said:A five year-old doesn't have much chance here, but I'll try to be basic...
This isn't like mixing two liquids together - the concept of an equilibrium temperature somewhere in between doesn't apply. A liquid freezes or a solid melts at one and only one temperature (per a given substance and pressure). If you add heat to ice (put it in a warmer liquid) it will melt at its melting temperature, period. If you remove heat from water, it will freeze at its freezing temperature, period. If those are different temperatures, the lower temperature wins because while the ice can exist as ice at a lower temperature than its freezing point, you can't remove heat from a liquid (by making it melt ice) without dropping its temperature.
This may seem like a bit of a contradiction, but it is actually somewhat similar to the simpler case of a liquid at its boiling point. There is only one boiling point at a given pressure and no matter how much heat you add, that won't change. Conversely, if you lower the pressure above a liquid (say, put it in a vacuum chamber), it will start to boil and that will lower the temperature to get it to the new boiling point.
russ_watters said:Keeping within the narrow question, the interesting/difficult/counterintuitive behavior is that both the ice and drink can cool down when you combine them if both start above the freezing point of the drink.
I'm not referring to dilution there, I'm referring to the existence of the solution (or not) in contact with the ice.DrStupid said:Why should no dilution produce different result than ignoring dilution (as assumed in your post #33)?
I gave an explicit example above:Daanh said:In what possible scenario would they both cool down? Assuming you wouldn't put them both in a deep-freezer...
You're looking at the scenario backwards: when ice melts, the act of melting removes heat and reduces the temperature of the remaining ice.Kevin McHugh said:Phase changes are isothermal and are either exo or endothermic. Water freezes at 0oC. Which is an endothermic process. The more heat you remove doesn't effect temperature of the phase change, but it does hasten the kinetics. Same as boiling water at 100oC, the more heat you put in, the faster the water boils, but never exceeds 100oC. Somebody mentioned freezing point depression. Mixtures of substances will have lowered freezing points, and elevated boiling points.
russ_watters said:If you add ice at 0C to a liquid which is at 10C, but has a freezing point of -5C, the final mixture will be both at about -5C (ignoring dilution).
The latent heat absorbed by the melting ice.Daanh said:When all the liquid is at zero degrees, what will make the temperature drop more?
russ_watters said:If you add ice at 0C to a liquid which is at 10C, but has a freezing point of -5C, the final mixture will be both at about -5C (ignoring dilution).
russ_watters said:4. Add 1/4 cup (60g) of table salt.
russ_watters said:The latent heat absorbed by the melting ice.
I think we are using the word "dilution" to refer to different things and the way I designed the experiment may have an impact there. When I say "dilution" I am referring to a change in the concentration of the liquid solution as the ice melts. In cases where the amount of melting ice is small compared to the amount of water, there is very little change in the concentration of the solution and hence very little change in the melting point of that solution. That's what I was referring to when I said I was ignoring dilution.DrStupid said:Without dilution the minimum temperature is 0 °C.
That's where the dilution comes into play. NaCl has a positive enthalpy of solution and reduces the freezing point of water. Without these effects the temperature cannot drop below 0 °C. As ethanol has a negative enthalpy of solution (according to http://sites.chem.colostate.edu/diverdi/C477/experiments/isothermal%20microcalorimetry/references/j_mol_struct_1993_v300_p539.pdf) that won't work with alcoholic drinks.
I'm not sure if I understand this: correctly: " Water freezes at 0oC. Which is an endothermic process." Freezing (liquid to solid phase change is an exothermic process), while melting is endothermic. Please correct me if I'm wrong.Kevin McHugh said:Phase changes are isothermal and are either exo or endothermic. Water freezes at 0oC. Which is an endothermic process. The more heat you remove doesn't effect temperature of the phase change, but it does hasten the kinetics. Same as boiling water at 100oC, the more heat you put in, the faster the water boils, but never exceeds 100oC. Somebody mentioned freezing point depression. Mixtures of substances will have lowered freezing points, and elevated boiling points.