The adsorption of vapours on mercury. IV. Surface potentials and chemisorption

Abstract

An apparatus has been constructed to measure the surface potential of adsorbed vapours on mercury. There was shown to be a change in potential of 0.055V at the phase change associated with the alteration in the orientation of toluene molecules adsorbed on the surface of the mercury. Carbon tetrachloride, hexachlorethane and chloroform vapours reacted with mercury, and the rate of the reaction was determined by the accompanying change in surface potential which was over 1V in the case of carbon tetrachloride. The kinetics indicated that the substances were dimerizing under the action of the mercury surface with negligible activation energy. The rate of reaction with carbon tetrachloride was in agreement with the calculated rate, assuming that the activated complex consisted of two physically adsorbed molecules loosely held together and able to move over the surface. Methyl iodide vapour was found to react with mercury only when illuminated with light from a mercury lamp. There was little change of surface potential associated with this reaction, but the kinetics were determined from the irreversible changes in the surface tension of the mercury. It was found that the rate of reaction depended on the square root of the light intensity, which suggested that the methyl iodide was being dissociated into radicals, which in turn reacted with the mercury.