Gas Compressibility Factor Interpretation

[Kakashi]

Z=Vreal gas/V ideal gas

An Ideal gase assumes the only interaction between molecules is that they elastically bounce off each other it ignores attractive/repulsive force intermolecular forces (except during collisions). Does this mean that the ratio of intermolecular distance to molecular size is large making interactions negligible?


For n mol of gas in a container at a certain T and P isnt Vreal the volume of the container? And V-ideal would be tte volume predicted from the ideal gas law.

If Vreal/Videal>1, does this imply that repulsive forces dominate? My understanding is molecules are closer, electron clouds overlap causes repulsion and so to maintain the same P (collisions with the vessel's walls) the system must expand to a larger volume?

 

[BvU]

Z=Vreal gas/V ideal gas

An Ideal gase assumes the only interaction between molecules is that they elastically bounce off each other it ignores attractive/repulsive force intermolecular forces (except during collisions). Does this mean that the ratio of intermolecular distance to molecular size is large making interactions negligible?

the ideal gas assumption also includes zero molecular volume. The ratio you mention doesn't exist.

To go from ideal gas $\ \displaystyle {\left ( {pV = nRT}\right)}\$ to real gas $\ \displaystyle {\left ( {pV = ZnRT}\right)}\$ two phenomena are brought in: molecular size and intermolecular force. Clearly illustrated in the van der Waals equation $$ \left ( p+{a\over{V_m^2}}\right )\left(V_m - b\right) = RT $$(actually not an equation but an approximation).

So I would stick to $\ \displaystyle Z = {p_{\rm real}V_{\rm real}\over{p_{\rm ideal}V_{\rm ideal}}}\$ and take it from there.

Note that intermolecular forces are often attractive (polar molecules). See Atkins: physical chemistry

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