# Volume of ideal gas molecule [closed]

Is there any reason as to why we assume the volume of ideal gas to be negligible in comparison to the container? What is the underlying reason to assume that the ideal gas molecules are point molecules? Why can we not assume them to be non-point particles?

• If you assume point particles and no inter-particle forces, as simplifying approximations, then you have an easy path to this useful approximation: pV = nRT, i.e., the ideal gas law. Of course, you can assume non-negligible particle sizes and assume that inter-particle forces exist, so then the equation of state will necessarily be more complicated. – Ed V Jan 26 at 17:02
• If it weren't negligible, we would expect different behavior of molecules of distinct size. However, the ideal gas law is not dependent on particle size. You might try to derive a gas law for uniform volume particles rather than zero-volume particles but then you would expect that chosen uniform volume to somehow appear in your alternative gas law (for example, the volume of the gas could not be smaller than the total volume of particles). In the ideal gas law, the volume of the gas approaches zero as the temperature approaches zero (with fixed n and p). – Karsten Theis Jan 26 at 17:28
• The experiment shows that boiling water at 100°C produces a vapor which is about $1000$ times more cumbersome that the liquid water from which it is produced. As in this process the molecules have not been chemically modified, it means that in the vapor, the volume occupied by the molecules is negligible, as if they were point particles. – Maurice Jan 26 at 17:28
• I'd use voluminous instead of cumbersome, but Maurice makes a good point. Chemistry typically uses 3 or 4 significant figures at best. The equation PV=nRT isn't going to yield 15 digits of precision. // Van der Waals equation makes some rudimentary corrections to the ideal gas equation. – MaxW Jan 26 at 17:59
• Saving the best for last [ ;-) ], see equation of state in wikipedia! Loads of increasingly complicated equations of state! Imagine being a beginning chemistry student and having all that dropped on you! Hence the practical reality that beginning chemistry courses are heavily simplified (and often seriously over-simplified) so as to be manageable and so that there are survivors! – Ed V Jan 26 at 18:34