Reactions of diatomic molecules. IV. Kinetics of formation of bromine chloride
Reactions of diatomic molecules. IV. Kinetics of formation of bromine chloride
复制标题
双原子分子的反应。
DOI：
10.1021/j100865a073
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发表时间：
1967
期刊：
影响因子：
--
通讯作者：
R. M. Noyes
中科院分区：
文献类型：
--
作者：
P. R. Walton;R. M. Noyes
结果由于溴在分析波长处的吸收比氯强得多，当氯过量时，一次运行中的吸收变化最大，大多数运行都是在这种条件下进行的。在75.6下进行的一系列这样的实验支持这样的假设，即在每种反应物中速率确实是一级的，并且对于溴比氯过量两倍的一次实验计算出相同的速率常数。对于一系列的运行在相同的温度下，其中氯和溴最初在相同的（和化学计量）浓度，计算的速率常数的变化与初始浓度近似成反比。这样的行为意味着总的阶数比1多一点，而不是预期的值2。在几个不同的温度下，0.06 M的氯和0.005 M的溴溶液的速率常数是0.04 M的卤素溶液的两倍以上。我们无法解释这些动力学异常，也无法推导出与所有观测结果一致的速率表达式。其中一种反应物过量的运行明确支持双分子机理的预期动力学，并且替代的原子链机理至少在动力学一致性方面是不令人满意的，并且由于下面讨论的原因也是站不住脚的。因此，报告的速率常数仅限于运行在不平等的反应物浓度。
Results Since bromine absorbs much more strongly than chlorine at wavelengths of analytical interest, the ab-sorbance change during a run was greatest when chlorine was the species in excess, and most runs were made for this condition. An extensive series of such runs at 75.6 supported the hypothesis that the rate was indeed first order in each reactant, and the same rate constant was computed for one run in which bromine was in twofold excess over chlorine. For a series of runs at the same temperature in which chlorine and bromine were initially in equal (and stoichiometric) concentrations, the computed rate constants varied approximately inversely with initial concentration. Such behavior implies that the over-all order is little more than 1 instead of the anticipated value of 2. At several different temperatures, the rate constant for a solution 0.06 M in chlorine and 0.005 M in bromine was over twice that for a solution 0.04 M in each halogen. We are unable to explain these kinetic anomalies or to derive a rate expression consistent with all of the observations. The runs in which one reactant was in excess definitely support the kinetics anticipated for a bimolecular mechanism, and the alternative atomic chain mechanism is at least as unsatisfactory with re-gard to kinetic consistency and is also untenable for reasons discussed below. The reported rate constants are therefore restricted to runs at unequal reactant concentrations.