Gas-phase reaction of mercury with ammonium iodide and hydrogen iodide

Journal Article · Thu Nov 02 04:00:00 EST 1978 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100511a001· OSTI ID:6566174

Jeannotte, A; Appelman, E H; Schreiner, F; Abraham, B A

The gas-phase reaction of mercury with ammonium iodide is the basis of at least one scheme for the thermochemical production of hydrogen. We have studied the reactions Hg + 2HI ..-->.. HgI/sub 2/ + H/sub 2/ and Hg + 2NH/sub 4/I ..-->.. HgI/sub 2/ + H/sub 2/ + 2NH/sub 3/ in the gas phase for 623 to 693 K. Under our conditions NH/sub 4/I is completely dissociated to NH/sub 3/ and HI. The reactions were followed by spectrophotometrically monitoring the buildup of the product, HgI/sub 2/. In the absence of NH/sub 3/ and with approximately 20-fold excess of HI (10/sup -3/ M equal to or less than (HI) equal to or less than 10/sup -2/ M), the rate of appearance of HgI/sub 2/ is given by d(HgI/sub 2/)/dt = k/sub 4/(Hg)(HI). With excess Hg, however, the rate follows the expression d(HgI/sub 2/)/dt = k/sub 5/(Hg)(HI)/sup 2/. Introduction of NH/sub 3/ into the system increases the rate substantially. In the presence of ammonia at concentrations comparable to those of the Hg and HI, the rate law assumes the form d(HgI/sub 2/)/dt = k/sub 3/(Hg)(HI)/sup 2/(NH/sub 3/). At 663 K k/sub 4/, k/sub 5/, and k/sub 3/ have the values 3.7 L mol/sup -1/ min/sup -1/, 590 L/sup 2/ mol/sup -2/ min/sup -1/, and 2.2 x 10/sup 6/ L/sup 3/ mol/sup -3/ min/sup -1/, respectively. Increasing the surface-to-volume ratio has no discernible effect on the reaction rate. The constant k/sub 3/ has a negative temperature dependence, which corresponds to an activation energy of -34 kJ/mol. The reaction in the presence of ammonia is interpreted in terms of a preequilibrium to form a complex HI . Hg . NH/sub 3/. 4 tables, 5 figures.

• Research Organization: Argonne National Lab., IL
• OSTI ID: 6566174
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 82:22; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
080102* -- Hydrogen-- Production-- Thermochemical Processes
ABSORPTION SPECTRA
ACTIVATION ENERGY
AMMONIA
AMMONIUM COMPOUNDS
AMMONIUM HALIDES
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
DISSOCIATION
ELEMENTS
ENERGY
HALIDES
HALOGEN COMPOUNDS
HIGH TEMPERATURE
HYDRIDES
HYDRIODIC ACID
HYDROGEN COMPOUNDS
HYDROGEN PRODUCTION
INORGANIC ACIDS
IODIDES
IODINE COMPOUNDS
KINETICS
MERCURY
MERCURY COMPOUNDS
MERCURY HALIDES
MERCURY IODIDES
METALS
MONITORING
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
QUANTITY RATIO
REACTION KINETICS
SPECTRA
STOICHIOMETRY
TEMPERATURE DEPENDENCE
THERMOCHEMICAL PROCESSES
YIELDS