Re: If I blow up a balloon out in space, would the air rush out if I let go?

Simply put, yes.  The pressure in space is very low compared to that inside 
a blown-up balloon.  As a result, the air would be forced out - provided 
that the balloon is not tied shut.  This is an example of the Second Law of 
Thermodynamics (Entropy), which states that energy flows from a higher 
state to a lower state, and cannot be returned to the higher state without 
doing work on the system (i.e., blowing-up the balloon again).  

Space does not contain air, as we know it here on Earth.  Space is a 
vacuum, having very low concentrations of the elements we call air.  Space 
is also filled with cosmic radiation, and in our solar system, the solar 
wind.  Solar wind is composed of particles ejected from the sun (protons, 
electrons, etc.).  

The Pressure on the surface of the Earth is 663.5 times greater than that 
at an altitude of 190-km (118-miles).  At this altitude an atomic particle, 
or ion, will travel 2,562,865,585 times further, before impacting another, 
than near the surface of the Earth.

Space possesses a great deal of atomic radiation, but not enough 
concentration of Nitrogen and Oxygen gases to constitute air.  Air is 21% 
Oxygen, 78% Nitrogen, and 1% other gases - this is assuming no smog, which 
adds many harmful gases to the mix.

Your friendly neighborhood Mad Scientist,

Dennis K. Van Gemert, M.S.A.E.