Thermal and photochemical studies of the system 18-molybdodiphosphate and iodide

✍ Scribed by D. Dimotikali; E. Papaconstantinou

• Book ID: 103993454
• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 354 KB
• Volume: 54
• Category: Article
• ISSN: 1010-6030
• DOI: 10.1016/1010-6030(90)87005-v

✦ Synopsis

1SMolybdodiphosphate [PzMo18062]6-, (MolS6-) and iodide react slowly until equilibrium is established Mols6-+21-+2H+= H2M0186-+ I, The reaction is first order with respect to molybdate and iodide, and seems to be first order with respect to H+ in the pH range of 0 to 2, where the molybdate is stable. Rate =~[I-][H+][Mo,~~-1, k= 3.9 x lo-* M-* s-' at 25 'C; E, = 68.4 kJ mol-' and AS= -48 J deg-' molml. The equilibrium constant is 2X 1W3. The thermal equilibrium shifts toward the reactants upon irradiation with light absorbed by the iodine and/or O-M"+ charge transfer bands, whereas the mixed valence absorption MS+ -0-M6+ (700 nm) is not photosensitive. The new equilibrium position, which reflects a balance between the photochemical and thermal reaction, depends on the wavelength and the light intensity. The equilibrium is re-established to the original position in the dark. The photolytic "cycIe" was repeated many times without decomposition of the system.