📚 Balancing Chemical Equations: KS3 CIE Answers | KS3 CIE 化学方程式配平：答案与解析
In KS3 CIE Chemistry, balancing chemical equations is a core skill. This revision guide explains the rules, shows worked examples, and provides answers to common practice questions.
在 KS3 CIE 化学中，配平化学方程式是一项核心技能。本复习指南讲解规则、展示例题，并提供常见练习题答案。
1. What is a Chemical Equation? | 什么是化学方程式？
A chemical equation uses symbols and formulas to show what happens in a chemical reaction. The starting substances are called reactants, and the new substances are called products.
化学方程式使用符号和化学式来表示化学反应中发生的变化。起始物质叫反应物，生成的新物质叫生成物。
Example | 示例：
H₂ + O₂ → H₂O
This tells us hydrogen reacts with oxygen, but it is not yet balanced because the number of atoms on each side is different.
这表示氢气与氧气反应，但尚未配平，因为两边的原子数不同。
In CIE worksheets, you may also be given a word equation first, such as 'hydrogen + oxygen → water', and asked to write the correct formulas before balancing.
在 CIE 练习中，你也可能先看到文字方程式，例如“氢气 + 氧气 → 水”，需要先写出正确的化学式，然后再配平。
2. Why Must Equations Be Balanced? | 为什么方程式必须配平？
Equations must be balanced because atoms cannot be created or destroyed in a chemical reaction. The total number of each type of atom must be the same on both sides.
方程式必须配平，因为在化学反应中原子不能被创造或消灭。每一种原子的总数在两边必须相同。
An unbalanced equation breaks the law of conservation of mass, which is a key CIE marking point. If atoms are not balanced, the equation does not describe a real reaction correctly.
未配平的方程式违反了质量守恒定律，这是 CIE 考试的重要得分点。如果原子数不平衡，方程式就不能正确描述真实反应。
3. The Law of Conservation of Mass | 质量守恒定律
The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. Therefore, the total mass of reactants equals the total mass of products.
质量守恒定律指出，在化学反应中质量既不会被创造也不会被消灭。因此，反应物的总质量等于生成物的总质量。
When balancing equations, only coefficients can be changed. A coefficient is a number placed before a formula. Never change the subscript inside a formula.
配平方程式时，只能改变系数。系数是写在化学式前面的数字。绝不能改变化学式中的下标。
For example, H₂O cannot become H₂O₂ just to balance oxygen atoms. That would change the substance itself.
例如，不能为了配平氧原子而把 H₂O 改成 H₂O₂，因为这会改变物质本身。
4. How to Balance Equations: The Four-Step Method | 配平方程式的四步法
Follow these steps to balance any KS3 CIE equation.
按照以下步骤可以配平任何 KS3 CIE 方程式。
- Step 1: Write the correct formula for each reactant and product. | 第一步：写出每种反应物和生成物的正确化学式。
- Step 2: Count the number of atoms of each element on both sides. | 第二步：数出两边每种元素的原子数。
- Step 3: Add coefficients in front of formulas to balance one element at a time. | 第三步：在化学式前添加系数，一次配平一种元素。
- Step 4: Check all elements again and make sure coefficients are in the lowest whole-number ratio. | 第四步：再次检查所有元素，并确保系数是最简整数比。
Using a small atom inventory table can help you avoid mistakes, especially when the same element appears in several formulas.
使用简单的原子数统计表有助于避免错误，尤其是当同一种元素出现在多个化学式中时。
5. Worked Example 1: Hydrogen + Oxygen → Water | 示例1：氢气 + 氧气 → 水
Unbalanced equation: | 未配平方程式：
H₂ + O₂ → H₂O
Count atoms: Left: H=2, O=2. Right: H=2, O=1. Only oxygen is unbalanced.
数原子：左边 H=2、O=2；右边 H=2、O=1。只有氧原子不平衡。
To balance oxygen, place coefficient 2 before H₂O: | 为配平氧，在 H₂O 前加系数 2：
H₂ + O₂ → 2H₂O
Now oxygen is balanced, but hydrogen has become 4 on the right. Add coefficient 2 before H₂ on the left.
此时氧已配平，但右边的氢变成了 4 个。在左边 H₂ 前加系数 2。
2H₂ + O₂ → 2H₂O
Check: Left: H=4, O=2. Right: H=4, O=2. This is the balanced answer.
检查：左边 H=4、O=2；右边 H=4、O=2。这就是配平后的答案。
6. Worked Example 2: Methane + Oxygen → Carbon Dioxide + Water | 示例2：甲烷 + 氧气 → 二氧化碳 + 水
Unbalanced: | 未配平：
CH₄ + O₂ → CO₂ + H₂O
Count: Left: C=1, H=4, O=2. Right: C=1, H=2, O=3. Carbon is already balanced.
数原子：左边 C=1、H=4
Published by TutorHao | KS3 Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图