Dissociation of hydrogen molecules

Chemisorption (i.e., absorption of hydrogen), which involves dissociation of hydrogen molecules into hydrogen atoms and chemical bonding of the atoms to a host matrix. Thus, the hydrogen is integrated in the lattice of a metal, an alloy or a chemical compound. 

The velocity will thus vary as the min power of the gas pressure. In the case of the dissociation of hydrogen molecules into atoms at the surface of a hot metal wire Langmuir found mln =, whilst for the recombination of atoms at a surface min was found to be 2. 

If the sorption and dissociation of hydrogen molecules is a rapid process, then the hydrogen atoms on the membrane surface are in equilibrium with the gas phase. The concentration, c, of hydrogen atoms on the metal surface is given by Sievert s law ... 

As shown in Fig. 5.1, since excited hydrogen atoms can be produced by dissociation of hydrogen molecules and molecular ions, the hydrogen molecules can affect emission from the hydrogen atoms. Therefore, by investigating emission from the hydrogen atoms, we can study hydrogen molecule behav-... 

Under experimental conditions when hydrogen gas is heated the decomposition of the molecules to atoms begins at approximately 2000 °C. Values for the equilibrium constant of the dissociation of hydrogen molecule, H2 < 2H, are... 

The chief objection to the Tafel theory is that it leads to an incorrect value of the slope h in equation (26). If the electrode surface is sparsely covered with atomic hydrogen, the rate of the reaction 2H = H2 will be proportional to n, where n is the number of adsorbed atoms per sq. cm. of surface. If the rate of the reverse process, i.e., the dissociation of hydrogen molecules into atoms, is negligible, the current flowing I will be proportional to the rate of the formation of molecular hydrogen, since the latter is assumed to be the slow process at the cathode. It follows, therefore, that I is equal to kn, where fc is a constant. The potential E of an atomic hydrogen electrode, neglecting activity influences, can be represented by the equation... 

The catalytic activity increased with time over 2-3 hours (at 323 K) and 70-90 min (at 373 K) followed by a period of relative stability. Naito et al. [23] have suggested that oxygen molecules on small gold particles behave as a peroxo-like adsorbed species, which enhances the dissociation of hydrogen molecules. Moreover, the products are similar to those obtained... 

Consider first the dissociation of hydrogen molecules into hydrogen atoms... 

Farkas and Farkas (81, 82) assumed that the rate of dissociation of hydrogen molecules on the catalyst was measured by the parahydrogen conversion. They further assumed that the hydride was adsorbed by dissociation of a hydrogen atom, and that hydrogen and hydride competed for the chemisorbed layer. 

The contribution of reaction (6-128) is especially important when generation of H atoms in the discharge is delayed with respect to the formation of N atoms. Such a kinetic delay can be due to a more effective N2 dissociation through vibrational excitation and contribution of dissociative attachment and electronic excitation to dissociation of hydrogen molecules. 

As for the solution-diffusion mechanism, the hydrogen permeation through a palladium layer is a complex process consisting of adsorption and dissociation of hydrogen molecules, followed by diffusion of hydrogen atoms through the metal... 

Hydrogen can permeate selectively dense metal membranes, behaviour that permits the separation of hydrogen from gas mixtures. The mass transfer mechanism consists of several steps dissociation of hydrogen molecules into atoms, interaction of hydrogen atoms with the metal surface and their adsorption, diffusion of hydrogen into the metal lattice, and desorption of hydrogen atoms from the other metal surface and their recombination into molecules.The overall transport process through the metal wall is called permeation and is ruled by the expression ... 

Hydrogen gas is bubbled into a hydrochloric acid solution at 25°C. The platinum electrode has two functions. First, it provides a surface on which the dissociation of hydrogen molecules can take place ... 

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