It will depend upon a number of factors espescially the mass of the gas molecules.

PV= 1/3 Nm v^2 (taking v as root mean square of speed)

so 1mole of gas occupies about 24dm^3 (24 x10^-3 m^3)at STP. assume the gas is Nitrogen - molar mass 0.028kg. (28 g)
rearranging: v^2= 3PV/Nm (Nm= No of mpolecules x mass or 1 molecule = molar mass) Take atmospheric pressure to be 1x10^5 Pa.

V^2 = 3 x 1x10^5 x 24 x 10^-3/ 0.028 =257140

v= 507/s So lets say about 500m/s.

(Notice - the gas molecules have to travel faster than the speed of sound - as it is the motion of the gas molecules that transmits the energy.)