The solubility of Cr(NO3)3-His-H2O system at 298.15K in the entire concentration range has been investigated by phase equilibrium method and the corresponding phase diagram has been constructed. The congruently soluble complexes Cr(His)(NO3)3·3H2O(A), Cr(His)2(NO3)3 ·3H2O(B) and Cr(His)3(NO3)3·3H2O(C) which have not been reported in literature, have been prepared. The compositions of these complexes are determined by chemical analyses and elemental analyses. The enthalpies of reaction of chromium nitrate with histidine in water have been measured by microcalorimeter. On the basis of experimental and calculated results, three thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), the rate constant, three kinetic parameters (the activation energy, the pre-exponential constant and the reaction order) are obtained.

Key words: CHROMIC NITRATE, HISTIDINE, PHASE DIAGRAM, HEAT CONTENT, PHASE EQUILIBRIUM, CHROMIUM COMPOUNDS, THERMODYNAMICS, THERMOCHEMISTRY