How is it possible that gases (helium especially) can leave a balloon or even a high-pressure tank over time ?

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How is it possible that gases (helium especially) can leave a balloon or even a high-pressure tank over time ?

In: Chemistry

Hydrogen and helium are very very smol atoms (the smallest they can be and still be called atoms, in fact). So they kinda just… slip through the gaps between larger atoms that form the container. They have an easier time doing that through something very thin, like a stretched balloon, but slowly they can find their way out of solid metal tanks.

When you’re down at the atomic scale there’s no such thing as a solid object but rather atoms and molecules. The rubber in a balloon is made of long molecules which are basically chains of atoms. These are all intertwined.
Think of it like a messy mass of chains.

However there are gaps between these chains big enough to let very small things though for example helium molecules.

The main molecules in “normal” air are nitrogen (N2) oxygen (O2) and carbon dioxide (CO2).
These molecules are simply too big to get through the small gaps in the molecular chains.

Helium is the literally the smallest gas available. It leaks more through smaller holes than other gasses. Rubber are long molecules intertwined, with lots of space in-between it. Gasses will naturally leak. Even water will leak (water will evaporate, then diffuse through the rubber).

Metal tanks are better, but high-pressure will make it more likely that stuff still escapes.