📚 Equilibria in Gas Reactions: The Equilibrium Constant Kp | 气体反应平衡：平衡常数 Kp
Chemical equilibria involving gases are a cornerstone of physical chemistry. Understanding how to quantify the position of equilibrium using partial pressures, rather than concentrations, is essential for reactions where all components are in the gas phase. The equilibrium constant expressed in terms of partial pressures, Kp, provides a direct link between the thermodynamics of the system and the measurable pressures of reactants and products. This article explores the concept of Kp, how it is derived from the ideal gas law, how to calculate and interpret its value, and how changing conditions affect equilibrium in gaseous systems, all aligned with the Cambridge International A-Level Chemistry syllabus.
涉及气体的化学平衡是物理化学的基石。对于所有组分都处于气态的反应，理解如何用分压（而非浓度）来定量描述平衡位置至关重要。以分压表示的平衡常数 Kp 在系统的热力学与反应物和产物的可测量压力之间建立了直接联系。本文探讨 Kp 的概念、如何从理想气体定律推导、如何计算和解释其数值，以及条件变化如何影响气体体系的平衡，内容完全符合剑桥国际 A-Level 化学大纲。
1. Introduction to Gaseous Equilibria | 气体平衡导论
In a closed system, many gas-phase reactions are reversible. At equilibrium, the rates of the forward and reverse reactions are equal, and the partial pressures of all species remain constant. For a general reaction aA(g) + bB(g) ⇌ cC(g) + dD(g), where a, b, c, and d are stoichiometric coefficients, we can define an equilibrium constant based on partial pressures, denoted as Kp. This constant is temperature-dependent and dimensionless only when the sum of the stoichiometric coefficients of products equals that of reactants; otherwise, it has units derived from pressure.
在密闭体系中，许多气相反应是可逆的。达到平衡时，正逆反应速率相等，所有物种的分压保持恒定。对于一般反应 aA(g) + bB(g) ⇌ cC(g) + dD(g)，其中 a、b、c、d 为化学计量系数，我们可以定义一个基于分压的平衡常数，记作 Kp。该常数依赖于温度，只有当产物化学
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