nonlinear gas versus linear gas?

Question

This is a physical chemistry question. What does it mean when it is said some property of "linear gas molecules" versus "nonlinear gas molecules"? How can you tell if the gas is linear or nonlinear?

Answer 1

While I suspect the first answer is pretty much what the question is targeting, it is conceivable they are talking about the SHAPE of the molecule.

A linear molecule (diatomic, or linear like CO2) will have different spectra and thermal properties (like heat capacity) compared to a non-linear structure because there is less degrees of freedom in the rotation. Rotation about the linear axis does not follow the equipartion of energy, like vibrations or rotations about a non-linear axis. You also don't see microwave spectra from rotation about this axis.

Polyatomic linear molecules however will have l-type doubling of their vibrational spectra.

Answer 2

A gas behaves linearly if the usual linear laws (Boyle, Charles) give accurate answers. At high pressures, the finite size of the molecules becomes important, and the linear equations work less well; this is said to be the non-linear region.

Answer 3

so for a picture of a linear gas molecule would be 0-0-0 and a non-linear would be like a triangular or not a straight line.

Answer 4

Linear could also be ideal and non-linear could be non-ideal. The answer above is very good