To convert a sample of air into a liquid as done commercially to produce liquid nitrogen, you would probably..
increase T, increase P, at room temperature 1)you are above the critical point for nitrogen and oxygen
2)decrease T, increase P
3)cool it to zero Kelvin
4) forget it; it cannot be done
Answer:
2 is correct.
In order to get a gas into a liquid, you need to compress down the molecules so that they are closer together and cannot move as quickly. It makes sense sense that decreasing temperature makes the molecules slower (think of how freakin cold liquid nitrogen is), and increasing pressure squeezes them closer together (hence storage containers for liquid nitrogen are really thick to handle the pressure).
2)
2
2 decrease T, Increase P
In fact the process to do such could involve compressing the air to a very high pressure. The process of compression also increases the temperature. You would allow the hot compress air to cool to ambient temperature (or colder if their is a cooler source) Allow the gas to go thru an orifice (free expansion) without allowing it to absorb more heat energy. Some of the gas will liquifey. The remainder can be either recompressed through another cycle or used as a coolant for the compression cycle.
The compression can go thru stages allowing cooling between stages. This would help efficiency.
Ans. 2). (Both to Critical Conditions).
(Once in liquid form, Nitrogen can be stored in specially insulated vessels at just above atmospheric pressure. Its boil-off will maintain the liquid temperature at -196°C).
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