📚 Year 8 AQA Chemistry: Formula & Theorem Quick Reference Handbook | AQA 化学公式定理速查手册
This handbook provides a concise summary of essential formulas, laws and calculation methods covered in the Year 8 AQA Chemistry curriculum. Mastering these fundamentals will help you tackle numerical problems, write balanced equations and understand the quantitative side of chemical reactions.
本手册速查囊括了 AQA 八年级化学课程中的核心公式、定律和计算方法。掌握这些基础知识，将帮助你解决数值计算问题、正确书写配平方程式，并理解化学反应的定量侧面。
1. Law of Conservation of Mass | 质量守恒定律
In a chemical reaction, the total mass of the reactants equals the total mass of the products. Atoms are neither created nor destroyed; they are only rearranged.
在化学反应中，反应物的总质量等于生成物的总质量。原子既不能被创造也不能被消灭，只会重新排列。
This means that if you start with 10 g of reactants, you must end up with 10 g of products (provided no gas escapes or enters the system). All chemical calculations rely on this fundamental law.
这意味着如果从 10 g 反应物开始，结束时也应有 10 g 生成物（前提是没有气体逸出或进入体系）。所有化学计算都依赖于这条基本定律。
2. Writing Chemical Formulae | 化学式的书写
The chemical formula of a compound shows the symbols of the elements present and the ratio of atoms. Use the periodic table to find symbols and apply the crossover rule for ionic compounds.
化合物的化学式表示所含元素的符号以及原子个数比例。利用元素周期表查找符号，对于离子化合物可采用交换下标法。
For covalent molecules, prefixes such as mono-, di-, tri- indicate the number of atoms (e.g. CO2 is carbon dioxide). Valency or combining power helps determine the formula: Mg2+ and Cl− → MgCl2.
对于共价分子，前缀如单、二、三表示原子个数（例如 CO2 是二氧化碳）。化合价或结合能力有助于确定化学式：Mg2+ 与 Cl− → MgCl2。
3. Balancing Chemical Equations | 化学方程式的配平
A balanced equation has the same number of each type of atom on both sides. Follow these steps: write the unbalanced equation, count atoms, add coefficients in front of formulas, and ensure all coefficients are in the simplest whole-number ratio.
配平的方程式两边各原子种类数目相同。遵循以下步骤：写出未配平的方程式，清点原子数，在化学式前添加系数，并确保所有系数为最简整数比。
Never change the subscripts in a formula to balance – that changes the substance. For example, H2 + O2 → H2O becomes 2H2 + O2 → 2H2O, not H2O2.
切勿通过改变化学式中的下标来配平——那样会改变物质本身。例如，将 H2 + O2 → H2O 配平为 2H2 + O2 → 2H2O，而不是写成 H2O2。
4. Relative Atomic Mass (Ar) | 相对原子质量
Relative atomic mass (Ar) is the average mass of an atom of an element compared with 1/12 the mass of a carbon‑12 atom. It is a ratio and has no unit.
相对原子质量（Ar）是某元素原子平均质量与一个碳‑12 原子质量的 1/12 相比较的比值，没有单位。
The Ar values are found on the periodic table and are often rounded to the nearest whole number for calculations at this level. For example, Ar of oxygen is about 16, and of magnesium is 24.
Ar 值可在元素周期表上查到，在此阶段的计算中常近似取整。例如，氧的 Ar 约为 16，镁的 Ar 为 24。
5. Relative Formula Mass (Mr) | 相对式量
For a compound, the relative formula mass (Mr) is the sum of the relative atomic masses of all the atoms in its formula. It has no unit.
化合物的相对式量（Mr）是其化学式中所有原子的相对原子质量之和，没有单位。
Example: Mr of H2O = (2 × 1) + 16 = 18. Mr of CaCO3 = 40 + 12 + (3 × 16) = 100. This value is used to calculate reacting masses and percentage compositions.
举例：H2O 的 Mr = (2×1) + 16 = 18。CaCO3 的 Mr = 40 + 12 + (3×16) = 100。这个值可用于计算反应质量和质量百分比。
6. Percentage by Mass of an Element in a Compound | 化合物中元素的质量百分比
% mass of element = (total mass of the element in one formula unit / Mr of compound) × 100%. This shows the proportion of each element by mass.
元素质量百分数 =（该元素在1个式单元中的总质量 ÷ 化合物的 Mr）× 100%。这显示了每种元素的质量占比。
For example, % of oxygen in H2O = (16 / 18) × 100% = 88.9%. In CO2, % of carbon = (12 / 44) × 100% ≈ 27.3% and % of oxygen ≈ 72.7%.
例如，水中氧的质量百分比 = (16 / 18) × 100% = 88.9%。在 CO2 中，碳的质量百分比 = (12 / 44) × 100% ≈ 27.3%，氧的质量百分比 ≈ 72.7%。
7. Reacting Mass Calculations (Ratio Method) | 反应质量的计算（比例法）
Using a balanced equation and Mr values, we can calculate the masses of reactants and products without using moles. This is often called the mass ratio method.
利用配平方程式和 Mr 值，我们可以在不使用摩尔的情况下计算反应物和生成物的质量，这常称为质量比法。
Steps: write the balanced equation, work out the Mr of each relevant substance, multiply by the balancing coefficients to get the total mass ratio, then set up a proportion.
步骤：写出配平方程式，计算各有关物质的 Mr，乘以配平系数得到总质量比，然后列出比例式。
Example: 2Mg + O2 → 2MgO. Mass ratio: 48 g Mg : 32 g O2 : 80 g MgO. If 2.4 g Mg reacts, mass of MgO formed = 2.4 g × (80/48) = 4.0 g.
示例：2Mg + O2 → 2MgO。质量比：48 g Mg : 32 g O2 : 80 g MgO。若 2.4 g Mg 反应，生成 MgO 质量 = 2.4 g × (80/48) = 4.0 g。
8. Common Reaction Patterns | 常见反应通式
Recognising reaction types helps predict products. Acid + Metal → Salt + Hydrogen gas. Acid + Alkali → Salt + Water (neutralisation). Acid + Carbonate → Salt + Water + Carbon dioxide.
识别反应类型有助于预测产物。酸 + 金属 → 盐 + 氢气。酸 + 碱 → 盐 + 水（中和反应）。酸 + 碳酸盐 → 盐 + 水 + 二氧化碳。
Metal + Oxygen → Metal oxide (oxidation). Displacement: more reactive metal + compound of less reactive metal → less reactive metal + new compound.
金属 + 氧气 → 金属氧化物（氧化反应）。置换反应：较活泼金属 + 较不活泼金属的化合物 → 较不活泼金属 + 新化合物。
For example: Fe + 2HCl → FeCl2 + H2; NaOH + HCl → NaCl + H2O; CaCO3 + 2HCl → CaCl2 + H2O + CO2.
例如：Fe + 2HCl → FeCl2 + H2；NaOH + HCl → NaCl + H2O；CaCO3 + 2HCl → CaCl2 + H2O + CO2。
9. Reactivity Series and Displacement | 金属活动性顺序与置换反应
The reactivity series lists metals in order of how vigorously they react: K, Na, Ca, Mg, Al, Zn, Fe, Pb, (H), Cu, Ag, Au. A more reactive metal will displace a less reactive metal from its compound.
金属活动性顺序按反应剧烈程度排列：钾、钠、钙、镁、铝、锌、铁、铅、（氢）、铜、银、金。较活泼的金属能将较不活泼的金属从其化合物中置换出来。
Example: Zn + CuSO4 → ZnSO4 + Cu. If no reaction occurs, the free metal is less reactive than the metal in the compound.
例如：Zn + CuSO4 → ZnSO4 + Cu。若没有反应发生，则游离金属的活泼性弱于化合物中的金属。
This order also explains the extraction of metals: very reactive metals are extracted by electrolysis; less reactive ones can be extracted by heating with carbon.
这个顺序也解释了金属的冶炼：极活泼金属需用电解法提取；较不活泼的金属可用碳加热还原。
10. Electron Configuration and Ions | 电子排布与离子
The electronic configuration of atoms follows the pattern 2,8,8,… for the first 20 elements. The number of electrons in the outer shell determines the charge of a simple ion.
前 20 号元素原子的电子排布遵循 2，8，8… 的规律。最外层电子数决定了简单离子的电荷。
Metals lose electrons to form positive ions (cations); non‑metals gain electrons to form negative ions (anions). The ionic charge can be predicted from the group number.
金属失去电子形成阳离子；非金属得到电子形成阴离子。离子电荷可由族序数预测。
Example: Na (2,8,1) → Na+ (2,8); Cl (2,8,7) → Cl− (2,8,8). The formula of an ionic compound ensures the total positive charge equals the total negative charge.
例如：Na (2,8,1) → Na+ (2,8)；Cl (2,8,7) → Cl− (2,8,8)。离子化合物的化学式要保证总正电荷等于总负电荷。
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