How pressure and temperature change(or remain constant) during free expansion of a gas and WHY....WHY......WHY.....WHY.

when gas is compressed(pressed) what happens is the space between the gas decreases and hence more collisions takes place within the gas molecules....results increase in temperature....don't think that increase in temp. means large amount of temp...no..its only small amount of temp.is increased...if the gas is expanded the pressure decreases results in decrease of temp as the gas molecules move away and collisions btwn them decrease....