📚 Energy Changes in Chemical Reactions | 化学反应中的能量变化
All chemical reactions involve energy changes. When a reaction happens, energy is either transferred to the surroundings or taken in from the surroundings. In KS3 chemistry, we call these two types of reactions exothermic and endothermic. Understanding these energy changes is important because they explain everyday processes from burning fuels to cooling sports injuries.
所有化学反应都涉及能量变化。当反应发生时，能量要么被传递给周围环境，要么从周围环境中被吸收。在 KS3 化学中，我们把这两种反应类型分别称为放热反应和吸热反应。理解这些能量变化非常重要，因为它们解释了从燃烧燃料到冷却运动损伤等日常过程。
1. What Are Energy Changes? | 什么是能量变化？
In a chemical reaction, the starting substances are called reactants and the new substances formed are called products. Atoms are rearranged when reactants change into products. This rearrangement involves transfers of chemical energy. Chemical energy is stored in the bonds between atoms.
在化学反应中，起始物质称为反应物，生成的新物质称为产物。当反应物变成产物时，原子会发生重新排列。这种重新排列涉及化学能的转移。化学能储存在原子之间的化学键中。
If the products store less chemical energy than the reactants, the leftover energy is released to the surroundings, often as heat. If the products store more chemical energy than the reactants, the extra energy must be taken in from the surroundings, often as heat or light.
如果产物储存的化学能比反应物少，剩余的能量就会释放到周围环境中，通常以热的形式。如果产物储存的化学能比反应物多，额外的能量就必须从周围环境中吸收，通常以热或光的形式。
2. Exothermic Reactions | 放热反应
An exothermic reaction is one that transfers energy to the surroundings. This energy is usually released as heat, but light and sound can also be produced. Because energy is transferred out, the temperature of the surroundings increases. If you touch the container, it may feel warm or even hot.
放热反应是将能量传递给周围环境的反应。这些能量通常以热的形式释放，但也可能产生光和声。由于能量向外传递，周围环境的温度会升高。如果你触摸容器，可能会感到温热甚至烫手。
Some exothermic reactions happen quickly and release a lot of heat, such as burning magnesium ribbon. Others happen more slowly, such as the rusting of iron, but they still release energy over a longer time.
有些放热反应发生得很快，并释放大量热量，例如镁条燃烧。另一些则发生得较慢，例如铁生锈，但它们仍会在较长时间内释放能量。
3. Endothermic Reactions | 吸热反应
An endothermic reaction absorbs energy from the surroundings. The energy is usually taken in as heat, so the reaction mixture gets colder. The container may feel cool to the touch. The temperature of the surroundings drops because energy is being removed from them.
吸热反应从周围环境中吸收能量。这些能量通常以热的形式被吸收，因此反应混合物会变冷。容器摸起来可能感觉凉爽。由于能量被从周围环境移走，周围环境的温度会下降。
It is important not to confuse endothermic with ‘cold’ reactions. Endothermic reactions need an energy input, but they are still chemical reactions and produce new substances.
重要的是不要把吸热反应与 ‘冷’ 反应混淆。吸热反应需要能量输入，但它们仍然是化学反应，并且会生成新物质。
4. Examples of Exothermic Reactions | 放热反应实例
Here are some common exothermic reactions you may meet in KS3:
以下是一些你在 KS3 阶段可能会遇到的常见放热反应：
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Burning fuels: CH₄ + 2O₂ → CO₂ + 2H₂O + energy
燃烧燃料：CH₄ + 2O₂ → CO₂ + 2H₂O + 能量
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Neutralisation: hydrochloric acid + sodium hydroxide → sodium chloride + water + energy
中和反应：盐酸 + 氢氧化钠 → 氯化钠 + 水 + 能量
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Respiration: glucose + oxygen → carbon dioxide + water + energy
呼吸作用：葡萄糖 + 氧气 → 二氧化碳 +
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