IGCSE Edexcel Chemistry: Mastering Chemical Equilibrium | IGCSE Edexcel 化学：化学平衡考点精讲

📚 IGCSE Edexcel Chemistry: Mastering Chemical Equilibrium | IGCSE Edexcel 化学：化学平衡考点精讲

Chemical equilibrium is a core topic in the IGCSE Edexcel Chemistry syllabus, explaining how reversible reactions reach a state of balance. Understanding dynamic equilibrium and Le Chatelier’s Principle allows you to predict how changes in conditions affect the yield of industrial processes like the Haber and Contact processes. This article provides a detailed revision guide covering all key concepts, common pitfalls, and exam-focused explanations to help you ace your chemistry exam.

化学平衡是 IGCSE Edexcel 化学大纲中的核心主题，它解释了可逆反应如何达到平衡状态。理解动态平衡和勒夏特列原理，你就能预测条件变化如何影响哈伯法和接触法等工业过程的产率。本文提供详细的复习指南，涵盖所有关键概念、常见错误和考试重点解释，助你在化学考试中取得高分。

1. Reversible Reactions | 可逆反应

A reversible reaction is one where the products can react together to reform the original reactants. The reaction proceeds in both forward and backward directions under the same conditions. The symbol ⇌ is used to show reversibility. For example, heating hydrated copper(II) sulfate: CuSO₄·5H₂O(s) ⇌ CuSO₄(s) + 5H₂O(g). Heating drives the forward reaction (dehydration), while adding water to anhydrous copper sulfate reverses the reaction, reforming blue hydrated crystals.

可逆反应是指产物能够再次反应重新生成原来的反应物的反应。在相同条件下，反应可以同时正向和逆向进行。用符号 ⇌ 表示可逆性。例如，加热五水合硫酸铜：CuSO₄·5H₂O(s) ⇌ CuSO₄(s) + 5H₂O(g)。加热促进正向反应（脱水），而向无水硫酸铜加水则逆转反应，重新形成蓝色水合晶体。

2. Dynamic Equilibrium | 动态平衡

Dynamic equilibrium is reached when a reversible reaction takes place in a closed system and the rate of the forward reaction equals the rate of the backward reaction. At equilibrium, the concentrations of reactants and products remain constant, but both reactions are still occurring continuously. It is dynamic, not static, because molecules are constantly reacting in both directions.

当可逆反应在封闭系统中进行，且正向反应速率等于逆向反应速率时，就达到了动态平衡。在平衡状态下，反应物和产物的浓度保持不变，但两个方向上的反应仍在持续进行。它是动态的，而非静态的，因为分子在不断地朝着两个方向反应。

It’s crucial to remember that equilibrium can only be established in a closed system where no substances can escape. If a product is removed as it forms, the reaction may go to completion rather than reaching equilibrium.

必须记住，平衡只能在封闭系统中建立，即没有任何物质可以逸出。如果生成物一产生就被移除，反应可能会进行到底而无法达到平衡。

3. Characteristics of Equilibrium | 平衡的特征

At equilibrium, the macroscopic properties (such as colour, pressure, concentration) remain constant. The system appears unchanging, but at the particle level, forward and backward reactions are happening at equal rates. The equilibrium can be approached from either direction: starting with reactants only or products only, the same equilibrium mixture will eventually be obtained under the same conditions.

平衡时，宏观性质（如颜色、压强、浓度）保持不变。系统看似静止，但在微粒水平上，正逆反应以相等的速率进行。平衡可以从任一方向趋近：只从反应物开始，或者只从产物开始，在相同条件下最终会得到相同的平衡混合物。

Another key feature is that equilibrium is sensitive to changes in concentration, temperature, and pressure (for gases). Changing any of these factors disturbs the balance and causes the equilibrium position to shift.

另一个关键特征是，平衡对浓度、温度和（气体的）压强的变化很敏感。改变这些因素中的任何一个都会打破平衡，使平衡位置发生移动。

4. Le Chatelier’s Principle | 勒夏特列原理

Le Chatelier’s Principle states that if a change is made to a system at dynamic equilibrium, the position of equilibrium will move to counteract the change and reduce its effect. This principle is used to predict the shift of equilibrium when concentration, temperature, or pressure is altered.

勒夏特列原理指出，如果对处于动态平衡的系统施加一个改变，平衡位置将会移动以抵消这种改变，减轻其影响。该原理用于预测当浓度、温度或压强改变时平衡的移动方向。

For example, if you increase the concentration of a reactant, the equilibrium shifts to the right (forward direction) to use up the added reactant and produce more product. Conversely, increasing the concentration of a

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