mean speed of molecules

The mean speed of hydrogen molecules at a temperature of 3100° Celsius in a closed room in a usual time frame (say one second) is 0 m/sec (the room is closed). Instantaneous mean speed of one hydrogen molecule along very short distance (comparable to it's size) at 3100° Celsius is near 9000 meter per second!

This molecule movement is what make possible transmission of the sound and usual pressure laws and sub Mach aerodynamic laws.

If you drill a small hole in the room's wall with a width around an atom size, hydrogen atoms will get off the closed room at a speed near the mean instantaneous speed and at 90° of the wall, but there will be only one at a time.

So according to Newton's law the impulse will be very small even if the exhaust speed is far above usual ones.

If you drill a large hole in the room's wall with a width of 10 cm, hydrogen atoms will get off the closed room at a speed near the mean instantaneous speed but at angles varying between 0+ degrees and 90° of the wall, with an average of 45° and a mean exhaust speed of half the mean instantaneous speed..

Formulaes for Exhaust speed

Instantaneous mean speed of one hydrogen molecule at various temperatures.

Celsius Temperature

-73

227

527

1127

1627

2127

2627

3127

Kelvin Temperature

300

600

900

1500

2000

2500

3000

3500

Instantaneous mean speed of a hydrogen molecule in m/sec

2726

3855

4721

6095

7038

7868

8619

9310

But this is not the exhaust speed, it's only the mean speed you can measure.