Wrong.
Gas molecules have mass and the average net velocity of the gas molecules before the system is opened is zero, as they are contained in a closed system.
Yes, they are compressed into a container and the only work they do is in resisting the pressure from each other in an equal and opposite action/reaction, meaning no real work is done but potential energy is stored.
Once the system is opened the molecules will exit the system and therefore will have an average net velocity in the direction of the opening.
Correct; as long as there is a resistant force acting against those expanding molecules coming from the container. This provides the resistance from that compressed molecule on molecule push which creates a squeeze back. This is where you get the psssssssssssssssssssssssst.
No reaction pressure and no psssssssssssst, just an orderly expansion under no pressure.
To change the velocity the molecules must have accelerated. To accelerate a force must have acted on the molecules.
The container HOLDS the compressed molecules. Open the container at any point and the molecules just expand from the front nearest the opening.
It would be just like footballs rolling out of a conveyor belt in orderly fashion. Like waiting your turn to leave a cinema being careful not to push hard into the next person or be pushed into by another person, hard.
Think of it like one expanded ball at the front having no external resistance, except the one directly behind it expands to touch that and so on and so on. Like a set of beads.
There's only expansion towards the opening and no reaction towards the opposite end.
Now imagine it all happening in a nano second.
By Newton's third the molecules must have created an equal and opposite force on the container. Thus the container accelerates in the opposite direction.
The only force on the container is the compression force in equal terms at the sides slowly expanding as each molecule expands out of the container front. They all expand together creating no work.
Free expansion specifically means the expansion of a gas in a closed system.
There's a lot of meaning's for closed systems. This one you are talking about is the markjo diagram, right?
The container of pressure opened up to a container with vacuum?
No work being done. It's not really a good example but if you say no work is done then how do you expect itr to be done in a supposed space vacuum?
The net velocity at the start is zero and the net velocity at the end is zero. THIS IS WHY THERE IS NO WORK DONE.
This makes no real sense to be fair.
In a rocket the gas does not have a net velocity of zero and therefore work is done.
This is not really saying anything, either.