Isotope effect in liquids as shown by tracer diffusion at 25°C of several labeled benzenes in benzene, chlorobenzene,n-octane, and cyclohexane, and the relationship to the isotope effect in solids

Mutual and tracer diffusion coefficients at 25°C are reported for the liquid systems perdeuterobenzene(${\mathrm{C}}_6$ ${\mathrm{D}}_6$)-chlorobenzene, benzene(${\mathrm{C}}_6$ ${\mathrm{H}}_6$)-chlorobenzene, ${\mathrm{C}}_6{\mathrm{D}}_6-n$-octane, ${\mathrm{C}}_6{\mathrm{H}}_6-n$-octane, ${\mathrm{C}}_6$ ${\mathrm{D}}_6$-cyclohexane, and ${\mathrm{C}}_6$ ${\mathrm{H}}_6$-cyclohexane. These data are compared with similar data previously obtained in this laboratory. All the data indicate a very slight isotope effect for tracer diffusion of benzene in benzene, in chlorobenzene, in $n$-octane, and in cyclohexane. Application to the above data of the equation usually used to describe the "isotope effect" in solids, indicates that diffusion in these systems may be governed to a large extent by the viscosity of the solvent.