The dissociation of hydrogen into atoms

Abstract

The energy loss from heated wires in various gases can be readily calculated by simple equations. For nitrogen and mercury vapor the results calculated in this way agree well with experimental results up to temperatures as high as 3500° K. With air and carbon dioxide similar agreement was obtained up to the melting point of platinum. In the case of hydrogen, however, there is agreement only up to about 2100° K. Above that the energy loss increases extremely rapidly so that at 3300° it is four or five times the calculated value. This is explained by assuming that hydrogen at very high temperatures is dissociated into atoms. The theory of the heat conductivity of a dissociating gas was developed. The heat of the reaction and the degree of dissociation at various temperatures was thus calculated and was found to agree well with van't Hoff's equation. Experiments at low pressures prove that the phenomenon is a true dissociation, which follows the law of mass action and that the volume of the dissociation products is approximately twice the volume of the original hydrogen. That is, the dissociation takes place according to the equation [formula omitted] There is much evidence that the dissociation is not electrolytic. Nitrogen, even at 3500° K, is not perceptibly dissociated at atmospheric pressure. That is, its dissociation does not exceed 5%, at 3500° K. The following quantitative results have been obtained. The heat of reaction at constant volume for [formula omitted]is 550,000 joules, or 130,000 calories. At constant pressure it would be approximately 575,000 joules, or 136,000 calories at 3000° K The degree of dissociation at any temperature, T, is given by the equation [formula omitted]Here p1 is the partial pressure of the hydrogen atoms (in atm.), and P is the total pressures (in atm.). From this equation the free energy of formation of hydrogen molecules from atoms can be calculated. © 1912, American Chemical Society. All rights reserved.