# How do we define “volume” of the gas undergoing free expansion in vacuum? [closed]

Usually volume occupied by the gas is defined as the the volume of the container, but as it expands freely (Joule's free expansion), we can't say anything about volume in a concrete sense as we don't have a rigid container. How do we think about this in a more concrete way?

• We would first need the criterium what is a gas and what is vacuum. – Poutnik Sep 10 '20 at 10:29
• What about $V \to \infty$? – Safdar Faisal Sep 10 '20 at 10:31
• I often see people talking about expansions in a vacuum , how do they do this without something to concretely call volume? – Buraian Sep 11 '20 at 10:56
• Particularly, it is undefined. – Poutnik Sep 13 '20 at 12:11