# Compression of air

1. Jul 13, 2004

### bozo the clown

If i compress air enough without altering temparature it will turn to liquid right ?

2. Jul 13, 2004

### chroot

Staff Emeritus
Yes, but air is not a pure substance. The various gases (nitrogen, oxygen, argon, carbon dioxide, water vapor, etc.) will all condense at different pressures.

- Warren

3. Jul 13, 2004

### omin

Do the gases that make up our air, when compressed, have a tendency to seperate, gather, form layers, etc. in some particular way?

4. Jul 13, 2004

### ArmoSkater87

not in gas form, in liquid form, they probably will form layers since they all have different densities

5. Jul 13, 2004

### ArmoSkater87

And by the way, for your original question, as you decrease volume (compress), the temperature drops without you having any influence on it except compresing it.
P_1/T_1=P_2/T_2

Last edited: Jul 13, 2004
6. Jul 13, 2004

### LURCH

Don't you have that backward? I believe temperature increases as a gass (or an assortment of gasses) is compressed.

7. Jul 13, 2004

### jamie

temperature of the air increases as the volume of the container decreases because the molecules would be travelling faster and bouncing off the sides of the container more frequently.
brownian motion

8. Jul 13, 2004

### ArmoSkater87

yea...ur right i dont know what i was thinking, i though of it backwards :D

9. Jul 13, 2004

### bozo the clown

does the energy required to compress the air ( say for arguments sake oxygen ) to turn to liquid = the energy required to turn to liquid using temperature alteration

10. Jul 14, 2004

### ArmoSkater87

good question

11. Jul 14, 2004

### omin

If the volume of the container decreases, then the inner surface area of the container decreases in which the molecules rebound. The mass of the molecules is consistent, why does the velocity increase when compression occurs? Shouldn't the velocity actually decrease, because of increased contact with the smaller surface area of the container increases which causes of loss of velocity to the container wall for every rebound a molecule makes? And wouldn't this result in a decrease in temperature?

12. Jul 14, 2004

### chroot

Staff Emeritus
Your fundamental mistake is assuming that the gas particles always lose kinetic energy when they hit the walls of the container. They don't. If the walls of the container (say, the metal tank wall) is at the same temperature as the gas, then its molecules have similar kinetic energies. The only difference is that the wall's atoms/molecules are tightly bound to each other and vibrate back and forth rather than flying around freely. Sometimes a collision will transfer some kinetic energy from a gas particle to a particle in the wall; sometimes the opposite will happen. The net result is thermodynamic equilibrium.

If every collision resulted in the gas particle losing energy (and the wall particle gaining it), you'd find that the gas inside any container rapidly approaches absolute zero, while the temperature of the wall rapidly rises. It wouldn't make any sense.

- Warren