| Popis: |
The rate constants for the reactions of electrons with biphenyl, pyrene, perylene and carbon tetrachloride in n-hexane can all be expressed by the relation k = 3·6(±1) × 10 14 exp [ −14,600(±1000) RT ] mol −1 dm 3 s −1 over the temperature range 300-185 K. These are considered normal diffusion-controlled reactions, the activation energy (in J mol−1) being that for electron diffusion. For reaction with oxygen, k = 5×10 12 exp ( −9600 RT ] and the relatively slower rate for oxygen thus derives from the pre-exponential factor not from a higher activation energy, and is explained in terms of a reversible electron addition. In iso-octane there is more variation with solute than in n-hexane. Forcarbon tetrachloride, biphenyl and oxygen the activation energies are 2000, 2800 and 3200 J mol−1, respectively, and the pre-exponential factors 1·5×1013, 4·0×1013 and 1·0×1012, respectively. The rate constant with pyrene does not follow the Arrhenius expression and is about twice those for carbon tetrachloride and biphenyl at room temperature. |
