Kinetic energy collision theory component

The influence of temperature on diffusion should not be confused with thermal diffusion, which leads to a separation of components with different molar masses Soret effect). The theory is complicated but can be explained as follows At a warmer location, all gas molecules gain the same kinetic energy (m/2v ) but the impulse of heavier molecules is higher (mv). Thus, at collisions, they penetrate deeper into the direction of the lower temperature than lighter ones. The separation causes a concentration gradient parallel (heavy molecules) or antiparallel with respect to the temperature gradient. Thermal diffusion is very slow and mostly negligible compared to ordinary diffusion, but is relevant for polymer characterization and enrichment of isotopes, for example, for uranium isotopes. 

The overall aim in this analysis is to determine a rough estimate of the transfer fluxes in dilute one-component gases using the elementary mean free path concept in kinetic theory. In this approach it is assumed that the only means for transport of information in the fluid is via molecular collisions. Due to the physical similarity of the flux phenomena of mass, momentum and energy, a common mathematical formalism is outlined (e.g., [104] app E [61] sect 3.4.2 [77] sect 3-4 [39] sect 2). 

---