Science Buddies: "Ask an Expert"

Hello every one
recently i was researching about some rules about gases because i was working on a machine that works pretty much with laws of gasses.
now one of my problems is that how to lower a tempreture of a gas in sudden move
after researching in many books and internet and some calculating myself i figured out a way to do it but the reason that im posting this is to ask you guys if my researches are right or not?
ok lets begin
i say when gases are in a high pressure the heat capacity will increase and if suddenly the pressure gets lower all the energy will transform to kinetic energy and the temp will decrease now lets say the primery pressure is like 12bar and the secondary pressure is about 1bar
by the way if my research are right it actually explains why we can have both hot breath and cold breath(blowing)
now my another Q is that how much pressure difference is needed to liquefy the gas?like CO2 or O2 or N2 ...
thank U all for reading the hole text!

Hi logan2357,

A good place to start with many questions about gases is the ideal gas law: PV = nRT

At this point, let's not worry about numbers and just play with this equation.
P = pressure
V = volume
n = number of moles (how many gas molecules you have
R = gas constant (a fixed number)
T = temperature

let's take for example, your "sudden move" on gas in a chamber-- you want to lower the temperature.

R is a constant and (assuming no gas leaks out or chemical reactions) n is constant.

So if you want to lower T,

PV = (nR)T (n and R are fixed)
this means PV has to get smaller to make T smaller.

We now have 2 easy options: We can keep P constant or keep V constant.

If we fix P and decrease V, T must decrease to make this equation work.
Similarly, if we fix V and decrease P... T must decrease to make the equation work.

-John