[charmcaster]

I've read and seen a video (courtesy : MIT) where it was advised not to reflux a closed system. I'm assuming that means not to close the top end of the condenser. So, if I want to reflux a reaction that needs an inert atmosphere, what do I do??

In the lab we attache an adapter (of sorts) with a nitrogen balloon .. but that's a closed system, right ?? Am I taking a risk of explosion ?? I've done it like a million times, and it's pretty standard practice where I'm from. So, is there an alternative

[fledarmus]

No, this is not a closed system (unless the change in volume of the atmosphere in the system is more than the balloon can handle). When the balloon expands, the volume of the system expands. Expanding the boundaries of the system is another way for systems to be open. The very small increase in pressure required to expand the balloon is not enough to blow the system apart, unless your balloons are incredibly strong.