Le Chatelier’s Principle | A-Level CIE 化学：勒夏特列原理 考点精讲

📚 Le Chatelier’s Principle | A-Level CIE 化学：勒夏特列原理 考点精讲

Le Chatelier’s Principle is a fundamental concept in chemical equilibrium that predicts how a system at equilibrium responds to external changes. It states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change and re-establish equilibrium. This principle is essential for understanding and manipulating chemical reactions in both laboratory and industrial contexts, such as the Haber and Contact processes.

勒夏特列原理是化学平衡中一个基础概念，用于预测处于平衡状态的系统如何对外界改变作出响应。该原理指出：如果动态平衡受到条件改变的干扰，平衡位置将移动以抵消这种改变，并重新建立平衡。这一原理对于理解和调控实验室以及工业中的化学反应至关重要，例如哈伯法和接触法。

1. Defining Le Chatelier’s Principle | 勒夏特列原理的定义

Le Chatelier’s Principle can be stated as: when a system at dynamic equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium shifts so as to oppose the change. The system will adjust the rates of the forward and reverse reactions until a new equilibrium is achieved. It is crucial to note that the principle only applies to systems that are at equilibrium, not to initial rate or driving force discussions.

勒夏特列原理可以表述为：当一个处于动态平衡的系统受到浓度、压力或温度的改变时，平衡位置将发生移动以抵抗这种改变。系统会调整正反应和逆反应的速率，直到达成新的平衡。必须注意该原理只适用于已处于平衡的体系，而不是用于初始速率或反应推动力的讨论。

At equilibrium, the macroscopic properties (such as colour, pressure, concentration) remain constant because the forward and reverse rates are equal. A disturbance makes one of the rates momentarily faster, causing a net change in composition until the two rates match again. Le Chatelier’s Principle provides a qualitative way to predict the direction of that net change.

在平衡时，宏观性质（如颜色、压力、浓度）保持不变，因为正逆反应速率相等。一个扰动会使其中一个速率瞬间加快，导致组成发生净变化，直至二者再次相等。勒夏特列原理提供了一个定性的方法来预测这个净变化的方向。

2. Effect of Concentration Changes | 浓度变化的影响

Adding a reactant to an equilibrium mixture increases the rate of the forward reaction, shifting the position of equilibrium to the right (product side) to consume the added reactant. Similarly, removing a product also shifts the equilibrium to the right to replenish the product. Conversely, adding a product or removing a reactant shifts the equilibrium to the left.

向平衡混合物中加入一种反应物会增加正反应速率，使平衡位置向右（产物一侧）移动以消耗加入的反应物。同样，移除一种产物也会使平衡向右移动以补充产物。相反，加入产物或移除反应物则使平衡向左移动。

Consider the equilibrium Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq). The solution has a blood-red colour due to FeSCN²⁺. Adding Fe³⁺ (e.g. as iron(III) nitrate) intensifies the red colour because the equilibrium shifts right, producing more FeSCN²⁺. Adding a chloride which can precipitate Fe³⁺ or removing FeSCN²⁺ would shift the equilibrium left, causing the colour to fade.

以平衡 Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq) 为例。溶液因 FeSCN²⁺ 而呈现血红色。加入 Fe³⁺（如硝酸铁）会使红色加深，因为平衡右移，生成了更多的 FeSCN²⁺。加入可沉淀 Fe³⁺

Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）