| Abstrakt: |
Kinetic and thermodynamic studies of reduction of Fe(III) acetohydroxamic acid ([Fe(III)-AHA]) complex by ascorbic acid (AA) was performed at pH values ranging from 3.00-4.50 ± 0.1 (ionic strength 0.2) and temperature 05.0 - 25.0 ± 0.5 °C. The redox reactions were studied, spectrophotometrically, under pseudo first order conditions of [AA] over the [Fe(III)-AHA] under the experimental conditions. The redox reaction was found to be highly pH dependent. The values of 2nd order rate constants (k2), at 25 °C and pH 3.0, 3.5, 4.0 and 4.5 were found out to be 2.3920, 2.1550, 2.0122, 1.7596 M -1s-1, respectively. At 20 °C the values were 1.7290, 1.4000, 1.3400, 1.2650 M-1s-1 at pH 3.0, 3.5, 4.0 and 4.5, respectively. The results at 15 °C and pH 3.0, 3.5, 4.0 and 4.5 were 1.1410, 0.9459, 1.0390, 0.9126 M-1s-1, respectively. While, the values of rate constants at 10 °C were 0.7847, 0.7697, 0.6810, 0.7096 M-1s-1 and at 5 °C were 0.6167, 0.5106, 0.4775, 0.4833 M-1s-1, respectively. In addition to that, the following rate law was evaluated. Rate = dp/dt = k2 [Fe(III)-AHA] [AA]. Moreover, the thermodynamic activation parameters of the reaction were also determined. The values of DEa# at pH 3.0, 3.5, 4.0 and 4.5 were found out to be 22.4058, 16.3243, 19.9636, 14.6050 J/mol, respectively. While, the values of DH# were 58.5056, 42.6258, 52.1288, 38.1363 J/mol, respectively at pH 3.0 to 0 4.5. Values of DS# were also evaluated as -23.0297, -68.7567, -37.8287, -84.1377 J/mol/K at pH 3.0, 3.5, 4.0 and 4.5, respectively. Kinetic and thermodynamic studies of reduction of Fe(III) acetohydroxamic acid ([Fe(III)-AHA]) complex by ascorbic acid (AA) was performed at pH values ranging from 3.00-4.50 ± 0.1 (ionic strength 0.2) and temperature 05.0 - 25.0 ± 0.5 °C. The redox reactions were studied, spectrophotometrically, under pseudo first order conditions of [AA] over the [Fe(III)-AHA] under the experimental conditions. The redox reaction was found to be highly pH dependent. The values of 2nd order rate constants (k2), at 25 °C and pH 3.0, 3.5, 4.0 and 4.5 were found out to be 2.3920, 2.1550, 2.0122, 1.7596 M -1s-1, respectively. At 20 °C the values were 1.7290, 1.4000, 1.3400, 1.2650 M-1s-1 at pH 3.0, 3.5, 4.0 and 4.5, respectively. The results at 15 °C and pH 3.0, 3.5, 4.0 and 4.5 were 1.1410, 0.9459, 1.0390, 0.9126 M-1s-1, respectively. While, the values of rate constants at 10 °C were 0.7847, 0.7697, 0.6810, 0.7096 M-1s-1 and at 5 °C were 0.6167, 0.5106, 0.4775, 0.4833 M-1s-1, respectively. In addition to that, the following rate law was evaluated. Rate = dp/dt = k2 [Fe(III)-AHA] [AA]. Moreover, the thermodynamic activation parameters of the reaction were also determined. The values of DEa# at pH 3.0, 3.5, 4.0 and 4.5 were found out to be 22.4058, 16.3243, 19.9636, 14.6050 J/mol, respectively. While, the values of DH# were 58.5056, 42.6258, 52.1288, 38.1363 J/mol, respectively at pH 3.0 to 0 4.5. Values of DS# were also evaluated as -23.0297, -68.7567, -37.8287, -84.1377 J/mol/K at pH 3.0, 3.5, 4.0 and 4.5, respectively. [ABSTRACT FROM AUTHOR] |
