I've got a really dumb question that maybe you can answer. Keep in mind the last time I was in a chemistry class was 10th grade (half my life ago)...
How is the boiling point of any of these elements determined? I cant imagine that we got some helium in its gaseous form and cooled it down below -267 degrees and then heated it up slowly to find out. Is there something about it's atomic makeup that allows that number to just be calculated? Thanks.
No one really answered your question so I'll give it a shot.
Increasing the pressure on a gas increases it's boiling point. If you have a lot of pure helium gas and a really good compressor you can increase the pressure until the boiling point is high enough to exceed the temperature of the gas, so now you have a liquid helium at an insane pressure.
Next, drop the pressure and stick a thermometer into the liquid. When you hit atmospheric pressure the liquid will be boiling, but boiling liquids don't exceed their boiling point/temperature so helium is going to be waaay cold.
You can see this yourself: take a can of dust off or butane, turn it upside down and spray a bit into a shot glass (do not drink or breathe, super toxic). Instead of an aerosol spray a liquid will come out and begin to boil in the process making the glass super cold...
So, what's happening here you may wonder? It's chemistry/physics in action. When a pot of water boils on your stove it takes the heat energy from the burner and uses it to change states from liquid to gas. If you pour liquid water onto a piece of hot metal it turns into steam (boiling) while cooling off the metal (removing heat).
So when you take any liquid and rapidly raise it above it's boiling point (due to pressure or temperature changes) it will lower the temperature around it in order to obtain the energy it needs to change states.
All that being said, compressed helium is the most abundant means of cooling for low-temperature purposes because of these properties.
By boiling compressed helium at room temperature and pressure we can make something that super cold -267 degrees, at least while the helium continues to boil.
> If you have a lot of pure helium gas and a really good compressor you can increase the pressure until the boiling point is high enough to exceed the temperature of the gas, so now you have a liquid helium at an insane pressure.
The critical temperature of Helium is 9.35 °R -- above that it will not be a liquid at any pressure. So we have to go through successive phases of compression (which heats it up), cooling via another cryogen (liquid nitrogen initially, then liquid hydrogen in subsequent passes), and expansion (at the right conditions, because of the oddities of the Joule-Thompson effect[0] for elements like Helium), in order to cool it enough to produce a liquid.
> How is the boiling point of any of these elements determined? I cant imagine that we got some helium in its gaseous form and cooled it down below -267 degrees and then heated it up slowly to find out.
Why not? That's relatively easy to do in any moderately equipped physics lab.
A lot of these macroscopic features of things are really, really hard to work out from microscopic details from first principles. Things like why is coal black, water wet, etc? Not a stupid question at all.
How is the boiling point of any of these elements determined? I cant imagine that we got some helium in its gaseous form and cooled it down below -267 degrees and then heated it up slowly to find out. Is there something about it's atomic makeup that allows that number to just be calculated? Thanks.