When discussing an idealized gas, it is generally acceptable to assume a non-relativistic regime unless specified otherwise. This assumption allows for the application of classical mechanics, where the relationship E=p^2/2m holds true. The non-relativistic approximation simplifies calculations and is valid under typical conditions for gases at standard temperatures and pressures. However, in extreme conditions, such as high velocities or low temperatures, relativistic effects may need to be considered. Overall, the non-relativistic assumption is a common and practical approach in statistical mechanics.
