化学专业英语 翻译（校准版）
33 化学反应速度
Introduction
介绍
In this chapter we look into how chemical reactions occur. The principal aspect we examine is the rate of a reaction, and we shall see how it. depends on the temperature and the concentrations of the species that are present.
在本章中，我们来看看化学反应是如何发生的。我们研究的主要的方面是反应速率，我们将看到温度和存在的物质的浓度是如何影响化学反应速率的。
There are two main reasons for studying the rates of reactions. The first is the practical importance of being able to predict how quickly a reaction mixture will move its equilibrium state: the rate might depend on a number of factors under our control, such as the temperatu
re, the pressure, and the presence of a catalyst, and, depending on our aims, we may be able to make the reaction proceed at an optimum rate. For instance, in an industrial process it might be economical for the reactions to proceed very rapidly; but not so rapidly as to produce an explosion. By contrast, in a biological process it may be appropriate for a reaction to proceed only slowly, and to be switched on and off at the demand of some activity.
研究反应速率的主要原因有两个。首先是具有实际重要性的一点，也就是能够预测反应混合物何时到达它的平衡状态：化学反应速率可能取决于一些我们控制之下的因素，如温度，压力，和催化剂的存在，而且，根据我们的目的，我们也许能够使化学反应以一个最佳的速度进行。比如，在工业流程中，可能由于化学反应进行得非常迅速从而带来经济效益，但是也不能太过迅速以至于产生爆炸。相反，在一个生物进程中，化学反应可能只有进行得缓慢才是合适的，并且反应根据一些生物活动的需求进行和停止。
The second reason for studying reaction rates (which, as we shall see, is closely bound up with the first) is that the study of rates can reveal the mechanisms of reactions. The term ‘m
echanism’ has two connotations in this context. The first is the analysis of a chemical reaction into a sequence of elementary steps. For example, we might discover that the reaction of hydrogen and bromine proceeds by a sequence of steps involving the fission of Br2 into two bromine atoms, the attack of one of these atoms on H2, and so on. The statement of all the elementary steps constitutes the statement of the mechanism of the reaction. The other meaning of mechanism relates to the individual steps themselves, and concerns their detailed nature. In this sense 'mechanism' concerns what happens as a bromine atom approaches and attacks a rotating, vibrating, hydrogen molecule.
研究反应速率的第二的原因(我们将在下文看到的,并与第一个原因息息相关)是研究可以揭示化学反应机制。在本文中“机制”这个词有两个涵义。首先是以基元反应的步骤去分析一个化学反应。例如,我们可能会发现氢和溴的反应是通过一连串的步骤组成的，这些步骤是Br2reaction kinetics mechanism期刊分裂成两个溴原子，然后再攻击H2的其中一个原子,等等。这个就是所有的化学反应都是由基元反应步骤构成的观点。“机制”的另一个涵义是关系到一个单独步骤的本身，以及,关注他们的具体性质。在这个涵义上的“机制”是关注当一个溴原子接近和攻击一个旋转、振动的氢分子时发生了什么。
The first type of analysis of mechanism is the central feature of classical chemical kinetics, and we concentrate on it in this chapter. The second type of analysis, called chemical dynamics, had to await the technological advances that made available molecular beams for the study of individual molecular collisions, and is discussed in the next chapter. The dividing line between chemical kinetics and chemical dynamics is not clear cut; crude models of individual reaction steps were built on the basis of kinetic analyses, and we see something of this in the present chapter.
第一种机制分析是经典化学动力学的核心特点，并且我们集中在这一章中讨论。分析的第二类型称为化学动力学,必须等待技术进步以提供研究单个分子的碰撞的分子束，并将在下一章加以讨论。经典化学动力学和化学动力学之间界限是不明显的,各个反应步骤大概的模型是建立在经典化学动力学分析的基础上,我们可以在本章看到。
Empirical chemical kinetics
经验化学动力学
The basic data of chemical kinetics are the concentrations of the reactants and products as functions of time. The method selected for monitoring the concentrations depends on the nature of the species involved in the reaction, and on its rapidity.
基本资料中的化学动力学是反应物和产物的浓度作为时间的函数。浓度的检测的方法的选择取决于自然物种参与的反应和他们的反应速度。
Many reactions go to completion (that is, attain thermodynamic equilibrium) over a period of minutes of hours, and may be monitored by classical techniques. One of the following methods is often chosen.
很多反应的完成（即热力学平衡）经过一段时间的分钟数或小时数，可以用经典方法来检测。下面的方法是常被选择的方法之一。
(1) Pressure changes. A reaction in the gas phase might result in a change of pressure, and so its progress may be monitored by recording the pressure as a function of time. An instance of this is the decomposition of nitrogen (V) oxide , N2O5, according to For every m
ole of N2O5 destroyed, 5/2 moles of gaseous products are formed. and so the pressure of the system increases during the course of the reaction. This method is inappropriate for reactions that leave the overall pressure unchanged, and for reactions in solution.
（1） 压力的变化。在气相中的反应也许会导致压力的变化，它的反应进度的检测可以通过记录压力作为时间的函数来进行。这是一个实例：五氧化二氮的分解，根据：(五氧化二氮的分解方程式)每反应1摩尔五氧化二氮，便有2.5摩尔气体生成，所以在反应过程中系统的压力会增加。这个方法不适合总体压力不变和在溶液中的反应。
(2) Spectroscopy. A technique that is available even when no pressure change occurs is the spectroscopic analysis of the mixture. For instance, the reaction can be followed by monitoring the intensity of absorption of visible light by the bromine.
（2）    光谱研究。光谱研究是一个即使没有压力的变化发生也依然有效的对混合物进行光谱分析的方法。例如：反应可以通过检测溴在可见光中强度的吸收被追踪。
(3)Polarimetrv. When the optical activity of a mixture changes in the course of reaction, it c
an be monitored by measuring the angle of optical rotation. This is a historically important method because its application to the hydrolysis of sucrose was the first significant study of the rate of a reaction (by Wilhelmy in 1850).
（3）    旋光计。当混合物的光学活动在反应过程中变化时，它可以通过测量光学的旋转角度的方法被检测。从历史上看这是一个重要的方法因为它对蔗糖水解的应用程序是对反应速率的第一个显著的研究。（威廉米，1850年）

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