1、0Lesson2 Chemical Equilibrium and Kinetics化学平衡和动力学A1 A major objective of chemist is to understand chemical reactions, to know whether under a given set of conditions two substances will react when mixed, to determine whether a given reaction will be exothermic or endothermic, and to predict the ext
2、ent to which a given reaction will proceed before equilibrium is established.化学家的一个主要目标是理解化学反应，知道在一组给定的条件下两种物质混合时能否发生反应；确定一个给定的反应是放热还是吸热；预测一个给定的反应在平衡前进行的程度。2 An equilibrium state, produced as a consequence of two opposing reactions occurring simultaneously, is a state in which there is no net change
3、 as long as there is no change in conditions. 平衡状态是由两个对立反应同时发生产生的结果，在平衡状态下，只要条件不发生改变，这个状态就不会有净变化。3 In this lesson it will be shown how one predict the equilibrium state of chemical systems from thermodynamic data, and conversely how the experimental measurements on equilibrium states provide useful
4、thermodynamic data. 在这节课中，将会展示如何根据热力学数据来预测化学体系的平衡状态，以及相反地，平衡状态下的实验测量值如何提供有用的热力学数据。4 Thermodynamics alone cannot explain the rate at which equilibrium is established, nor does it provide details of the mechanism by which equilibrium is established. 仅凭热力学无法解释平衡建立的速度，也不能提供平衡建立的详细的机理。5 Such explanations
5、 can be developed from considerations of the quantum theory of molecular structure and from statistical mechanics. 从分子结构的量子理论和统计力学的角度考虑可以使这样的解释得到发展。B1 To appreciate fully the nature of the chemical equilibrium state, it is necessary first to have some acquaintance with the factors which influence re
6、action rates. 要充分理解化学平衡状态的本质，首先需要对影响反应速率的因素有一定的了解。2 The factors which influence the rates of a chemical reaction are temperature, concentrations of reactants(or partial pressures of gaseous reactants), and presence of a catalyst.影响化学反应速率的因素有温度、反应物浓度（气体反应物的分压）和催化剂。3 In general, for a given reaction t
7、he higher the temperature, the faster the reaction will occur. 通常，对于一个给定的反应，温度越高，反应发生的越快。4 The concentrations of reactants or partial pressure of gaseous reactants will affect the rate of reaction, an increase in concentration or partial pressure increases the rate of most reactions.反应物浓度或气体反应物的分压将影
8、响反应的速率，对于大部分反应来说，增大浓度或分压，反应速率增大。5 Substances which accelerate a chemical reaction but which themselves are not used up in the reaction are called catalysts. 可以加快反应速率但本身不参加反应的物质称为催化剂。C1 Dynamic Equilibrium 动态平衡2 In many cases, direct reactions between two substances appear to cease before all of eith
9、er starting material is exhausted.许多情况下，两种物质间的直接反应在任意一种原始物料耗尽之前就会停止。3 Moreover, the products of chemical reactions themselves often react to produce the starting materials.而且，化学反应自身的产物能够发生反应生成原始物料。4 For example, nitrogen and hydrogen combine at 500 in the presence of a catalyst to produce ammonia: N
10、2+3H2=2NH31例如，在催化剂存在下，氮和氢在 500能够反应生成氨：5 At the same temperature and in the presence of the same catalyst, pure ammonia decomposes into nitrogen and hydrogen: 2NH3=3H2+ N2在相同温度和相同催化剂存在的条件下，纯净的氨气能够分解生成氮气和氢气：6 For convenience, these two opposing reactions are denoted in one equation by use of a double
11、arrow: 23NHA为了方便起见，这两个对立的反应能够用双箭头表示在一个方程式中：7 The reaction proceeding toward the right is called the forward reaction; the other is called the reverse reaction.向右进行的反应称为正反应，另外一个称为逆反应。D1 If either ammonia or a mixture of nitrogen and hydrogen is subjected to the above condition, a mixture of all the t
12、hree gases will result. 如果将气氨或氮气和氢气的混合物放在上述条件下，将会产生三种气体的混合物。2 The rate of reaction between the materials which were introduced into the reaction vessel will decrease after the reaction starts; 如果将原料放入反应器中，在反应开始后，反应速率将会降低；3 because their concentrations are decreasing, conversely, after the start of t
13、he reaction the material being produced will react faster, since there will be more of it.因为它们的浓度在减小，相反，在反应开始后，产物之间的反应将会加快，由于它们的浓度在增加。4 Thus the faster forward reaction becomes slower, and the slower reverse reaction speeds up.因此，较快的正反应会变慢，较慢的逆反应会变快。5 Ultimately the time comes when the rates of the
14、forward and reverse reactions become equal, and there will be no further net change. 最后，正反应和逆反应速率相等，且不再有进一步净变化的时刻终于到来。6 This situation is called equilibrium. 这种状态叫做平衡。7 Equilibrium is a dynamic state because both reactions are still proceeding; but since the two opposing reactions are proceeding at
15、equal rates, no net change is observed. 平衡是动态的，因为两个反应仍在进行；但由于两个对立反应进行的速率相等，所以观察不到净变化。E1 All chemical reactions ultimately proceed toward equilibrium. 所有的化学反应最后都要向平衡状态进行。2 In a practical sense, however, some reactions go so far in one direction that the reverse reaction cannot be detected, and they a
16、re said to go to completion. 然而，实际上，一些反应在一个方向上进行的很快以至于检测不到逆反应，他们被认为是进行完全的反应。3 The principles of chemical equilibrium apply even to these, and it will be seen that for many of them, the extent of reaction can be expressed quantitatively. 化学平衡的原理甚至也适用于这些反应（被认为是进行完全的反应） ，显然许多这类反应，其反应程度可以定量地表达。F1 Equili
17、brium Constants平衡常数2 Equilibrium is a state of dynamic balance between two opposing processes. For a general reaction at a given temperature: A+B=C+D平衡是两个相反过程的动态平衡状态。在给定温度下，对于一个普通的反应：23 At the point of equilibrium, the following ratio must be a constant: CDABK在平衡时，以下比值肯定是一个常数：4 The constant, K, is c
18、alled the equilibrium constant of the reaction. 常数 K 叫做反应的平衡常数。5 It has a specific value at a given temperature. 在一个给定温度下，它有一个比值。6 If the concentration of any of the components in the system at equilibrium is changed, the concentrations of the other components will change in such a manner that the d
19、efined ratio remains equal to K as long as the temperature does not change. 如果平衡时体系中任意组分的浓度改变，那么只要温度不变，其他组分的浓度将以保持相等 K 的固定比例的方式变化。7 The equilibrium constant expression quantitatively defines the equilibrium state. 平衡常数表达式定量地定义了平衡状态。8 More generally, for the reversible reaction aAbBcCdD更普遍的是,对于一个可逆反应
20、：9 The equilibrium constant expression is written as follows:cabK平衡常数表达式可以写成下面的形式:10 By convention, the concentration terms of the reaction products are always placed in the numerator of the equilibrium constant expression. 按照惯例，在平衡常数的表达式中，反应产物浓度项通常是放在分子的位置上。11 It should be noted that the exponents
21、of the concentration terms in the equilibrium constant expression are the coefficients of the respective species in the balanced chemical equation. 应该注意的是，在平衡常数表达式中浓度项的指数是平衡化学方程式中各自的系数。G1 Chemical Kinetics 化学动力学2 When a system is in the equilibrium state, the rate of the forward reaction is identica
22、l to the rate of the reverse reaction. 当一个体系达到平衡状态时，正反应的反应速率等于逆反应的反应速率。3 It is important to know just how fast a reactant is being used up in a process, or the speed with which a product is being formed.重要的是，要知道在反应过程中，反应物消耗完的速率，或者产物生成的速率。4 It is also important to have detailed information about rate
23、s of reactants in order to test theories and mechanisms for various kinds of chemical processes. 同样重要的是，要有关于反应物反应速率的详细信息，以便测试各种化学过程的理论和机理。5 Experiments show that a number of reaction variables affect reaction rates: 实验表明，许多反应变量都影响反应速率：H1 Temperature. The rates of chemical reactions are temperature-d
24、ependent. 温度。化学反应的速率是随温度变化的。2 Therefore, it is common practice when studying the rate in the laboratory to carry out reactions at constant temperature(isothermally), thus eliminating one variable. 因此，通常的做法是，当在实验室研究速率时，在恒温条件下完成反应，这样可以排除一个变量。I1 Pressure and Volume. Pressure is important in a kinetic c
25、onsideration of gas phase reactions.压力和体积。对于气相反应，压力是动力学中要考虑的一个重要因素。2 Usually, volume is fixed by running the reaction in container of fixed dimensions. 通常，体积是固定的，因为反应是在有固定容积的容器内进行的。33 For solid and liquid state reactions, pressure is usually atmospheric, and the volume of the reacting system is rela
26、tively unimportant because there is little change in volume. 对于固态和液态的反应，压力通常是大气压，反应体系的体积相对不重要，因为体积的变化很小。J1 Concentration. At any particular temperature, the rates of most chemical reactions are functions of the concentrations of one or more of the components of the system. 浓度。在任意一个指定的温度下，大多数的化学反应速率都
27、是体系中一个或多个组分浓度的函数。2 In practice, it is usually the concentration of the reactants that are used in determining the overall rates of reaction. 实际上，通常是用反应物的浓度来确定反应的总速率。K1 Catalyst. Any substance that affects the rate of a chemical reaction but cannot be identified as a product or reactant is said to be
28、 a catalyst. 催化剂。任何影响化学反应速率，但又不是产物或反应物的物质叫做催化剂。2 Catalyst may accelerate the rate, but we usually refer to decelerating catalysts as inhibitors. 催化剂可以加快速率,但我们通常把减慢反应速率的催化剂叫做抑制剂。L1 The order of a chemical reaction is given by the number of atomic or molecular species whose concentrations directly determine the reaction rate. 化学反应的顺序是由原子或分子种类的数目决定的，他们的浓度直接决定反应速率。M1 The rate of hydrolysis of acetate in water is directly proportional to the ethyl acetate concentration, the reaction is said to be first order. 乙酸酯在水中的水解率与乙酸乙酯的浓度直接成比例，这个反应叫做一级反应。
