大学化工专业英语Lesson 2

Chemical Equilibrium and Kinetics

化学平衡和动力学

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 extent 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，知道在给定的一组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放热还是吸热；预测一个给定的反应在平衡前进行的程度。

An equilibrium state, produced as a consequence of two opposing reactions occurring simultaneously, is a state in which there is no net change as long as there is no change in conditions.

两个相反的反应同时进行时的状态叫做平衡状态，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。

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 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，平衡状态的实验测量如何提供有用的热力学数据。

Thermodynamics alone cannot explain the rate at which equilibrium is established, nor does it provide details of the mechanism by which equilibrium is established.

单纯的热力学无法解释建立平衡的速度，也不能提供平衡建立所遵循的机理信息。

Such explanations 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。

To appreciate fully the nature of the chemical equilibrium state, it is necessary first to have some acquaintance with the factors which influence reaction rates.

要充分理解化学平衡状态的性质，首先必须熟知影响反应速率的因素。

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。 In general, for a given reaction the higher the temperature, the faster the reaction will occur.

一般来说，对于一个给定的反应，温度越高，反应速率越大。

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影响反应的速率，对于大部分反应来说，增大浓度或分压，反应速率增大。

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。

Dynamic Equilibrium

动态平衡

In many cases, direct reactions between two substances appear to cease before all of either starting material is exhausted.

在许多情况下，两种物质间的直接反应在所有原始物料耗尽之前就会停止。 Moreover, the products of chemical reactions themselves often react to produce the starting materials.

此外，化学反应自身的产物能够发生反应生成原始物料。

For example, nitrogen and hydrogen combine at 500 ℃ in the presence of a catalyst to produce ammonia:

N 2+3H 2=2NH 3

例如，在催化剂存在下，氮和氢在500℃能够反应生成氨：

N 2+3H 2=2NH 3

At the same temperature and in the presence of the same catalyst, pure ammonia decomposes into nitrogen and hydrogen:

2NH 3=3H 2+ N 2

在相同温度和相同催化剂存在下，纯净的氨能够分解生成氮和氢：

2NH 3=3H 2+ N 2

For convenience, these two opposing reactions are denoted in one equation by use of a double arrow:

22

3N 3H 2NH