I have recently been reading about why a can of compressed air gets cold when the air it contains is discharged. From what I understand the change from a liquid to a gas requires energy and therefore heat is drawn from the surrounding environment.
What confuses me is how the phase change sucks up heat? If energy is required to complete the phase change wouldn't that mean that the phase change would not take place unless heat was added? I guess I am confused as to how the phase change extracts the heat from the surrounding environment.
If I wanted to compress a gas into a liquid I would have to use force or my own energy to accomplish this, yet when going from liquid to gas the energy is just taken from the surrounding environment. This is confusing to me.