Measuring Enthalpy Changes: Calorimetry and Calculations | 测量焓变：量热法与计算

📚 Measuring Enthalpy Changes: Calorimetry and Calculations | 测量焓变：量热法与计算

In A-Level Chemistry, measuring enthalpy changes is one of the core practical skills. It links the theoretical idea of energy transfer in chemical reactions to simple laboratory data such as temperature change, mass, and specific heat capacity.

在A-Level化学中，测量焓变是一项核心实验技能。它将化学反应中能量转移的理论概念与温度变化、质量、比热容等简单的实验数据联系起来。

1. What Is Enthalpy and Enthalpy Change? | 什么是焓与焓变？

Enthalpy, H, is the total heat content of a chemical system at constant pressure. In practice, we cannot measure absolute H, but we can measure the heat change when a reaction occurs under constant pressure, called the enthalpy change, ΔH.

焓（H）是化学体系在恒压下的总热含量。实际中我们无法测量绝对焓值，但可以测量恒压下发生反应时的热量变化，即焓变ΔH。

The symbol ΔH is expressed in kilojoules per mole, kJ mol⁻¹. A negative ΔH means heat is released to the surroundings; a positive ΔH means heat is absorbed from the surroundings.

焓变符号ΔH的单位是千焦每摩尔（kJ mol⁻¹）。ΔH为负表示向环境释放热量；ΔH为正表示从环境吸收热量。

2. Exothermic and Endothermic Reactions | 放热反应与吸热反应

An exothermic reaction transfers thermal energy from the system to the surroundings, so the surroundings get hotter and ΔH is negative. Combustion, neutralisation, and displacement of a less reactive metal by a more reactive metal are common examples.

放热反应将热能由体系传递给环境，因此环境温度升高，ΔH为负。燃烧、中和以及活泼金属置换较不活泼金属都是常见例子。

An endothermic reaction absorbs thermal energy from the surroundings, so the surroundings get colder and ΔH is positive. Dissolving ammonium nitrate, thermal decomposition of carbonates, and some salt dissolutions are typical examples.

吸热反应从环境吸收热能，因此环境温度降低，ΔH为正。硝酸铵溶解、碳酸盐热分解以及某些盐的溶解都是典型例子。

3. Standard Conditions and Standard Enthalpy Changes | 标准状态与标准焓变Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com

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