Heat and Entropy of Sublimation of Nickel Dichloride, Dibromide, and Dihyphen;iodide; Dissociation Energies of Gaseous NiCl2and NiBr2

摘要

The vapor pressures of solid anhydrous nickel dichloride, dibromide, and dihyphen;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 withRin calories/molemiddot;degree and p and pgr; in atmospheres are as follows: NiCl2(550deg;ndash;608deg;C):RTlnpthinsp;equals;thinsp;minus;thinsp;lpar;53.59thinsp;plusmn;thinsp;0.41rpar;thinsp;times;thinsp;103thinsp;plus;thinsp;lpar;43.70thinsp;plusmn;thinsp;0.48rpar;T, at 855deg;Klogpthinsp;equals;thinsp;minus;thinsp;4.1472thinsp;plusmn;thinsp;0.0020; RTlnpgr;thinsp;equals;thinsp;minus;thinsp;lpar;52.76thinsp;plusmn;thinsp;0.40rpar;thinsp;times;thinsp;103thinsp;plus;thinsp;lpar;42.63thinsp;plusmn;thinsp;0.46rpar;T, at 855deg;Klogpgr;thinsp;equals;thinsp;minus;thinsp;4.1670thinsp;plusmn;thinsp;0.0019. NiBr2(519deg;ndash;584deg;C):RTlnpthinsp;equals;thinsp;minus;thinsp;lpar;53.01thinsp;plusmn;thinsp;0.76rpar;thinsp;times;thinsp;103thinsp;plus;thinsp;lpar;45.11thinsp;plusmn;thinsp;0.95rpar;T, at 820.16deg;Klogpthinsp;equals;thinsp;minus;thinsp;4.2595thinsp;plusmn;thinsp;0.0036; RTlnpgr;thinsp;equals;thinsp;minus;thinsp;lpar;51.97thinsp;plusmn;thinsp;0.27rpar;thinsp;times;thinsp;103thinsp;plus;thinsp;lpar;43.73thinsp;plusmn;thinsp;0.33rpar;T, at 820.16deg;Klogpgr;thinsp;equals;thinsp;minus;thinsp;4.2843thinsp;plusmn;thinsp;0.0014. Nil2(462deg;ndash;505deg;C):RTlnpthinsp;equals;thinsp;minus;thinsp;lpar;35.58thinsp;plusmn;thinsp;0.36rpar;thinsp;times;thinsp;103thinsp;plus;thinsp;lpar;32.60thinsp;plusmn;thinsp;0.52rpar;T; RTlnpgr;thinsp;equals;thinsp;minus;thinsp;lpar;37.39thinsp;plusmn;thinsp;0.24rpar;thinsp;times;thinsp;103thinsp;plus;thinsp;lpar;34.93thinsp;plusmn;thinsp;0.34rpar;T. For the chloride and the bromide, the measured pressures are 1.05(plusmn;thinsp;0.02) times the equivalent mass effusionlpar;pgr;rpar;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 areDgr;Fdeg;blpar;NiCl2,grpar;thinsp;equals;thinsp;minus;thinsp;180 000thinsp;plus;thinsp;54.78TandDgr;Fdeg;blpar;NiBr2,grpar;thinsp;equals;thinsp;minus;thinsp;131 000thinsp;plus;thinsp;38.22Tboth in calories/mole. The derived dissociation energies to the gaseous atoms are 7.8 eV for NiCl2(g) at 850deg;K and 5.7 eV for NiBr2(g) at 820deg;K. The absolute entropy of gaseous NiCl2at 850deg;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 dihyphen;iodide cannot be accomplished because significant but unknown amounts of gaseous NiI and I2are present causing transport back and forth between the cell and its surroundings.