1. Many years ago I saw a show where they examined oxygen forming into ice crystals on the sides of an industrial meat freezer, but thinking about that now, it seems ludicrous. How would they get the temperature low enough in there to get it to freeze? Does oxygen even become snow, and at what temperature?

2.

3. The melting point of oxygen is 54.8 K (-218.3ºC or -360.9ºF) a little bit too low for an industrial meat freezer.

Best regards,

César

4. Forgive my lack of knowledge, but is freezing and melting the same thing in the case of oxygen?

5. Originally Posted by Zipline
Forgive my lack of knowledge, but is freezing and melting the same thing in the case of oxygen?

6. In any case:

1. melting and freezing are opposite changes of state
2. melting point and freezing point are the same temperature; usually only the first denomination is used and it is defined as the temperature at which the liquid and solid phases of a substance of specified composition are in equilibrium at atmospheric pressure.

Best regards,

César

7. i persume its the same for any compound/element.

if its a solid, its molocules dont have the energy to move free. at 54.8K oxygen molocules have the energy to begin to move.

its melting point. if you go the other way, its freezing at this point,

8. Originally Posted by goodgod3rd
i persume its the same for any compound/element.

if its a solid, its molocules dont have the energy to move free. at 54.8K oxygen molocules have the energy to begin to move.

its melting point. if you go the other way, its freezing at this point,
Yay, someone explained it in simple english without Jargon. *hands prize*

9. 1. melting and freezing are opposite changes of state
As I thought, but you can never be too careful.

Originally Posted by goodgod3rd
its melting point. if you go the other way, its freezing at this point,
So, in other words, I need to make it warmer to freeze it? If freezing and melting occur at the same temperature, don't we get into Schrödinger’s Cat?

10. Originally Posted by Zipline
1. melting and freezing are opposite changes of state
As I thought, but you can never be too careful.

Originally Posted by goodgod3rd
its melting point. if you go the other way, its freezing at this point,
So, in other words, I need to make it warmer to freeze it? If freezing and melting occur at the same temperature, don't we get into Schrödinger’s Cat?
No no. He means that 54.8K is the melting point, and -54.8k would be the freezing point. I think.

11. Good, good. The reason I'm asking all this is that I'm writing a planet into a story that has oxygen snow at the poles. Algae on the equatorial sea produce oxygen, which travels to the colder regions and freezes. Is this feasible? Could humans live on the sparse (15% of the globe) land at the equator?

12. The melting point of water is 0ºC. What does it mean? It means that at that temperature liquid water begins to become a solid and solid water (ice) begins to become a liquid, i.e., two phases (liquid and solid) are in equilibrium. If the ice is becoming a liquid it is melting, if the liquid a solid, freezing. Melting and freezing are changes of state, being solid and liquid two different states.
The same applies to oxygen but at -218.3ºC.

Regarding your planet, Zipline, it must be a very cold planet to have -218ºC at the poles. Assuming that it is the size of Earth and that it has an equivalent atmospheric pressure (to be able to use the same terrestrial data) the human population could live in the frozen (water) equator getting energy from the wind and the planet´s internal heat. Oxygen could be produced by lichens which are able to live in extreme conditions, even in outer unprotected space.

The European Space Agency has discovered that lichens can survive unprotected in space. In an experiment led by Leopoldo Sancho from the Complutense University of Madrid, two species of lichen – Rhizocarpon geographicum and Xanthoria elegans – were sealed in a capsule and launched on a Russian Soyuz rocket on 31 May 2005. Once in orbit the capsules were opened and the lichens were directly exposed to the vacuum of space with its widely fluctuating temperatures and cosmic radiation. After 15 days the lichens were brought back to earth and were found to be in full health with no discernable damage from their time in orbit.
Source

Best regards,

César

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