Lewis Hartswick writes:

The case of venting it into vacuum is the same as venting it to
atmosphere.

I disagree. Nothing to push against, no force, no work, no heat. Just
eternal expansion.

I think I see another like my dad. He always said a rocket would not
work
in space since there was nothing to "push against". :-)

Mocking one's father is just wrong, like your physics.