The equilibrium pressure of ammonia over strontium ammoniate, Sr(NH3)6, has been measured at 18 temperatures extending from minus; 18 to 7deg;C. The standard enthalpy, free energy (at 0deg;C), and entropy of dissociation,Srlpar;NH3rpar;6lpar;srpar;equals;Srlpar;srpar;plus;6NH3lpar;grpar;, per mole of ammonia have been determined to be9.74plusmn;0.15kcal,1.68plusmn;0.02thinsp;kcal, and29.5plusmn;0.6eu, respectively. Combining the enthalpy of dissociation with other thermodynamic quantities, the gaseous formation energy of the strontium hexammine complex,Sr2plus;lpar;grpar;plus;6NH3lpar;grpar;rarr;Srlpar;NH3rpar;62plus;lpar;grpar;, is found to be minus;256 kcal/mole. This value is qualitatively consistent with the electrostatic theory of coordination complexes in which the ligand molecules are assumed to have progressively greater induced dipoles as the central ion diminishes in size.
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