Gas-Phase NMR Study of the DCl-HBr Isotope Exchange Reaction

Abstract

A physical chemistry laboratory experiment is described in which proton and deuteron FT-NMR spectra are used to determine the equilibrium constant for the isotope exchange reaction DCl + HBr <==> DBr + HCl . The measurement illustrates an unusual gas phase application of NMR spectroscopy. The results are in good accord with a 297K value of Kp = 0.818, calculated from statistical thermodynamics using vibrational-rotational constants. The latter can be taken from the literature or can be conveniently determined in a high resolution FTIR experiment commonly done in most physical chemistry laboratories.

Composition Determination of Low-Pressure Gas-Phase Mixtures by 1H NMR Spectroscopy

“…Despite its wide use for the analysis of liquid-phase mixtures, NMR spectroscopy has been used to analyze gas-phase mixtures in only a few cases. − Of those, only one study tested the accuracy of the method with a well-defined gas mixture, and that study was also the only one that reported measurement uncertainties for the NMR analysis. In that work, a gravimetrically prepared, 10-component natural gas surrogate (with light hydrocarbons ranging from methane to hexane, as well as CO 2 ) was analyzed.…”