How come nitrogen can stay so cold in all temperatures? I guess it’s not cold when compressed inside the bottle, rather a reaction when turning to gas? But where does the energy from the “room temperature” go?
In: Chemistry
You should ask why liquid nitrogen is so cold. That’s really what you meant to ask. The reason is because we make the nitrogen cold on purpose.
Nitrogen at normal atmosphere is a gas, not a liquid. By squeezing air (which is mostly nitrogen), it heats up. Then, while still squeezed (high pressure), you let it cool down. Then you re-expand the air. Expanding compressed air causes it to lose heat the same way that squeezing it causes it to generate heat. So now you have very cold air. So cold that the nitrogen is liquid at certain pressures.
Why is it liquid? The phase transitions from solid to liquid to gas relate to heat (and also pressure). A hotter thing is easier to make a gas. A cooler thing is easier to make solid. Because heat is just how much energy there is in the material vibrating and moving randomly. Lots of energy = hot = lots of motion = like a gas (each particle is zipping around freely). Low energy = cold = not much motion = staying in place like a solid.
So after going through the process, the nitrogen is cold enough to be liquid.
Nitrogen, like basically any matter, has no inherent temperature. When you see liquid nitrogen, it is extremely cold. Thats why there is so much steam coming off it. Thats nitrogen boiling off, as in, being heated to room temperature and turning into its gas state bc its boiling point is below room temp and normal pressure. It can be stored at these low temperatures in special containers but in a normal bottle it would heat up to the outside temp just like a bottle of any other gas or liquid.
Question: I don’t know what you mean. The atmosphere is 78% nitrogen and that’s all “room temperature”, relative to where its at. No molecule has an inherit temperature.
EDIT: Radioactive molecules may increase the temperature of things around them, but any stable molecule doesn’t hold onto any certain temperature.
> Sorry. If you keep a container of compresses nitrogen in the backing sun for 5 hours and then open it and pour it on your face, your face will get cold. Why is your face cold?
DO NOT EVER DO THIS! (Unless you know what you’re doing)
Liquid Nitrogen is dangerous, and should be handled with care. You don’t just leave a random compressed liquid nitrogen container baking in the sun. There is a real risk of it exploding and hurting people and destroying property.
> I guess it’s not cold when compressed inside the bottle, rather a reaction when turning to gas?
It is COLD! I think you are thinking about the lots of online videos when people are pouring liquid nitrogen into stuff, or dipping stuff into liquid nitrogen and getting to freeze in a snap. In all of these cases, the liquid nitrogen is NOT compressed, and it is COLD.
This is a dangerous substance, please handle it with care. This is why you need a certification / training to handle it, buy it, and transport it. You cannot be in elevator with it, you cannot use the stairs while carrying it. You have to book the elevator, put it in, let it travel to the desired floor alone, have another person there so that no one accidentally goes into the lift. Because you it spills while there’s someone in the elevator, the liquid nitrogen will evaporate, the temperature will drop, and the oxygen will be pushed away, and people will die. Same thing with car. You always put uncompressed liquid nitrogen in the trunk, never in the same area with the passenger. And you also keep it uncompressed. Because the pressure built up will be great, and most containers will explode.
So how does it stays cold? Well, it doesn’t. Just like how you buy a 5kg pack of ice, load it into the car, and after an hour of driving, some have melt, but not completely. The same deal with liquid nitrogen, it is always evaporating to gas. And after a while, it will be gone.
It’s the energy of phase change that keeps liquid nitrogen cold.
The point is, it is slowly turning to gas (evaporating). This evaporation takes energy so all the heat transferred from the environment to the nitrogen is used. The gas-liquid mixture can’t get above the boiling temperature until all the liquid is evaporated (for given pressure).
It is exactly the same reason that keeps boiling water at 100% centigrade no matter how much you heat it. 100C is the boiling point of water, just like nitrogen boiling point is -196C.
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