Let's try again.
Quote from Frenat:
that still does not touch on the molecules that are moving AWAY from the side opened to vacuum when it is opened.The molecules that are not rushing towards the side to the vacuum is used to apply forward force or the ACTION to the rocket. The REACTION is the exhaust particles rushing into a vacuumThis NASA illustration explains it rather well.

In aerospace engineering, the principal of action and reaction is very important. Newton's third law explains the generation of thrust by a rocket engine. In a rocket engine, hot exhaust gas is produced through the combustion of a fuel with an oxidizer. The hot exhaust gas flows through the rocket nozzle and is accelerated to the rear of the rocket. In re-action, a thrusting force is produced on the engine mount. The thrust accelerates the rocket as described by Newton's second law of motion.
As we learned earlier from Mainframe and I believe you agree,
"Gas molecules will all be flying around in random directions, in a pressurised container, exerting force equally on all sides of that container. If you were to then remove one side, then the gas molecules already moving towards that side would fly into the vacuum and exert no force."Ref:
https://exploration.grc.nasa.gov/education/rocket/newton3r.htmlWe are all told by NASA that space is a vacuum.
http://quest.nasa.gov/space/teachers/suited/3outer.htmlPhysics along with most sources defines vacuum as such.
Vacuum Physics
Vacuum, Space in which there is no matter or in which the pressure is so low that any particles in the space do not affect any processes being carried on there. It is a condition well below normal atmospheric pressure and is measured in units of pressure (the pascal). A vacuum can be created by removing air from a space using a vacuum pump or by reducing the pressure using a fast flow of fluid, as in Bernoulli’s principle.
I underlined the part that is most important. Basically it says that exhaust particles in space have no effect on the work they are being asked to do. In other words they do nothing to cause a rocket to move.
I can agree with Mainframe when he said, "Gas molecules will all be flying around in random directions, in a pressurised container, exerting force equally on all sides of that container. If you were to then remove one side, then the gas molecules already moving towards that side would fly into the vacuum and exert no force."
This is how physics definitions what the end results will be when you are trying to get any particle to do work in a vacuum.
This cycle will continue during the whole time the engine is running, exerting no force. The engine will run until it runs out of fuel or if it is stopped. If the engine is stopped and then restarted at a later time. The same cycle as before will begin all over again.
Gas molecules will all be flying around in random directions, in a pressurised container, exerting force equally on all sides of that container. If you were to then remove one side, then the gas molecules already moving towards that side would fly into the vacuum and exert no force.
Very simple isn't it?