Heat and Entropy of Sublimation of Nickel Dichloride, Dibromide, and Di-iodide; Dissociation Energies of Gaseous NiCl2 and NiBr2

Publisher Website
Google Scholar
Abstract
The vapor pressures of solid anhydrous nickel dichloride, dibromide, and di‐iodide have been measured directly by measurement of the torsional recoil of a suspended effusion cell and indirectly by measurement of mass effusion. The results with R in calories/mole·degree and p and π in atmospheres are as follows: NiCl2(550°–608°C): RT lnp = − (53.59 ± 0.41) × 103 + (43.70 ± 0.48)T , at 855°K logp = − 4.1472 ± 0.0020; RT lnπ = − (52.76 ± 0.40) × 103 + (42.63 ± 0.46)T , at 855°K logπ = − 4.1670 ± 0.0019 . NiBr2(519°–584°C): RT lnp = − (53.01 ± 0.76) × 103 + (45.11 ± 0.95)T , at 820.16°K logp = − 4.2595 ± 0.0036; RT lnπ = − (51.97 ± 0.27) × 103 + (43.73 ± 0.33)T , at 820.16°K logπ = − 4.2843 ± 0.0014 . Nil2(462°–505°C): RT lnp = − (35.58 ± 0.36) × 103 + (32.60 ± 0.52)T; RT lnπ = − (37.39 ± 0.24) × 103 + (34.93 ± 0.34)T . For the chloride and the bromide, the measured pressures are 1.05(± 0.02) times the equivalent mass effusion (π) for a molecular weight corresponding to the monomeric dihalide. This deviation from unity cannot be attributable to lack of information about the gaseous species but probably represents a demonstrable systematic difference between the two procedures. The free energies of bonding derived from the measurements are ΔF°b(NiCl2, g) = − 180 000 + 54.78T and ΔF°b(NiBr2, g) = − 131 000 + 38.22T both in calories/mole. The derived dissociation energies to the gaseous atoms are 7.8 eV for NiCl2(g) at 850°K and 5.7 eV for NiBr2(g) at 820°K. The absolute entropy of gaseous NiCl2 at 850°K is 85.4 eu, a value which yields an estimated 13.3 eu for the vibrational and electronic degrees of freedom. An analysis of the results for nickel di‐iodide cannot be accomplished because significant but unknown amounts of gaseous NiI and I2 are present causing transport back and forth between the cell and its surroundings.

This publication has 16 references indexed in Scilit: