Dry Ice Question

[Daitokuji]

The freezing point of CO2 is -109.3 °F or -78.5 °C which means it's hella colder than the freezing point of water. So why when you put dry ice in water the water doesn't freeze?

[Dolemite]

The water heats up the ice, noob. The freezing point of CO2 (which dry ice is simply the solid form of) is 109.3 °F, after all.

[Rated E]

Well, when dry-ice breaks down it turns into a gas, I was going to say that maybe the sublimation subtracts the cold temp from the water, but that doesn't make sense if you still have a block of dry-Ice sitting in the water.

But I read that water behaves differently when you change the pressure, changing the boiling and freezing point. Maybe the dry-ice alters the water pressure so the freezing point isn't the same.

[Burky]

I haven't studied this for a few years, but here's a rough explanation:

Any body above absolute zero has energy. As it gets hotter, its' energy increases.

It's about the specific heat capacity of the ice compared with the water.
SPC is the amount of energy required to raise 1kg of matter by 1 degree.
Water has a very high spc, which means it takes a lot of energy to raise/lower it by 1 degree.
CO2 on the other hand has a low spc, which means it doesn't take a lot of energy to raise/lower it by 1 degree.

Now what will happen when you put dry ice in water is that they will exchange energy between the two bodies until they are equal in temperature.
So consider what happens in this case. Suppose the water takes 10x the energy to change by 1 degree in temperature than the dry ice does (I made this figure up, it is not at all accurate). Then for every 10 degrees the dry ice rises, the water will drop by just 1 degree.
So suppose the dry ice heats up roughly by 100 degrees C, then the water will drop by just 10 C. So the water will in fact cool down, but only by 10 C in this case (it won't have frozen). But the dry ice will be long gone.

Things also get slightly more complicated, as it takes an extra amount of energy on top of the amount for the change in temperature in order for something to change state, i.e. from solid to liquid, liquid to gas or indeed solid to gas.

Rated E is correct in what he says above. The spc of something varies with pressure, and in particular, when you go higher up, the boiling point of water decreases.

[Anal Kaboom]

uh huh

[Drewbacca]

A better question to ask is why you'd even want to make regular ice when you already had super ice.

[Mr-K]

I like to get red dixie cups they have at frat parties filled with water and put dry ice in it, then walk around and offer it to girls.

[Doc Holliday]

The answer is simple, Dry Ice is Jesus Magic.

After drinking wine, he'll piss dry ice, store it in styrofoam containers, then hide it in the grocery store as treasure for the stockers to find. They in turn sell it to you, you put it in the water to look cool, and the water doesn't freeze, why? --because the water's not magic.