📚 Year 9 Cambridge Chemistry: Formulas and Theorems Quick Reference | Year 9 Cambridge 化学：公式定理速查手册
This quick-reference handbook brings together the essential formulas, definitions, and key principles you will meet in Year 9 Cambridge Chemistry. Use it alongside your class notes and practical work to build confidence in calculations, equation writing, and explaining chemical behaviour. Every statement is kept concise and matched with worked examples where helpful.
这本速查手册汇集了 Year 9 剑桥化学课程中必须掌握的公式、定义和核心原理。你可以将它和课堂笔记、实验记录配合使用，从而在化学计算、方程式书写和解释化学现象时更加自信。每个表述都力求简明，并在适当时配上典型示例。
1. Atomic Structure and Relative Atomic Mass | 原子结构与相对原子质量
Every atom contains a central nucleus made of protons and neutrons, surrounded by electrons arranged in shells. The atomic number (Z) is the number of protons and determines the element. The mass number (A) is the total number of protons plus neutrons: A = Z + N, where N is the neutron count.
每个原子都有一个由质子和中子组成的中心原子核，核外电子分层排布。原子序数 (Z) 等于质子数，它决定了元素的种类。质量数 (A) 则是质子数与中子数的总和：A = Z + N，N 代表中子数。
tomic mass, Aᵣ = (average mass of one atom of the element) / (1/12 × mass of one ¹²C atom)
相对原子质量 Aᵣ = (元素一个原子的平均质量) / (一个 ¹²C 原子质量的 1/12)
The electronic configuration is written as a series of numbers, e.g. sodium (Z=11): 2,8,1.
对于中性原子，电子数等于质子数。电子按 2, 8, 8, ... 的顺序填入电子层（前四周期）。电子排布写作一串数字，例如钠 (Z=11)：2,8,1。
2. The Mole, Molar Mass and Molar Volume | 摩尔、摩尔质量与摩尔体积
(Avogadro constant). The molar mass (M) of a substance is the mass of one mole of that substance; its unit is g/mol and its numerical value equals the relative formula mass (Mᵣ) in grams.
摩尔 (mol) 是物质的量的 SI 单位。1 摩尔精确包含 6.02 × 10²³ 个指定粒子（阿伏伽德罗常数）。物质的摩尔质量 (M) 是 1 摩尔该物质的质量，单位为 g/mol，其数值等于相对式量 (Mᵣ) 的克数。
Amount (mol) = mass (g) / molar mass (g/mol) n = m / M
物质的量 (mol) = 质量 (g) / 摩尔质量 (g/mol) n = m / M
At room temperature and pressure (rtp, 20 °C and 1 atm), one mole of any gas occupies a volume of 24 dm³. Therefore: n = V(dm³) / 24. This allows conversion between volume of gas and amount in moles.
在常温常压下 (rtp, 20 °C, 1 atm)，任何气体 1 摩尔的体积均为 24 dm³。因此：n = V(dm³) / 24。这一关系可用于气体体积与物质的量之间的换算。
3. Solution Concentration | 溶液浓度
The concentration of a solution tells us how much solute is dissolved in a given volume of solvent. The standard unit used is mol/dm³ (often written as M). The key formula linking moles, concentration and volume is:
溶液的浓度表示在一定体积溶剂中溶解了多少溶质。常用单位为 mol/dm³（常记作 M）。联系物质的量、浓度和体积的关键公式为：
ation (mol/dm³) = amount of solute (mol) / volume of solution (dm³) c = n / V
浓度 (mol/dm³) = 溶质的物质的量 (mol) / 溶液的体积 (dm³) c = n / V
Remember that volume must be expressed in dm³; if you are given cm³, divide by 1000 first. Also, the mass concentration in g/dm³ can be found from: c(g/dm³) = c(mol/dm³) × M. These relationships are essential for titration calculations.
注意体积必须以 dm³ 为单位；若题目给的是 cm³，需先除以 1000。此外，质量浓度 (g/dm³) 可通过 c(g/dm³) = c(mol/dm³) × M 求得。这些关系是滴定计算的基础。
4. Writing and Balancing Chemical Equations | 化学方程式的书写与配平
rated by an arrow (→). The law of conservation of mass states that atoms are neither created nor destroyed, so the number of each type of atom must be the same on both sides of the equation.
化学方程式用符号和分子式表示反应过程。反应物写在左侧，生成物写在右侧，中间用箭头 (→) 连接。质量守恒定律指出原子既不会凭空产生也不会消失，因此方程式两边每种原子的个数必须相等。
The balancing process involves placing large numbers (coefficients) in front of formulae. State symbols are added in brackets: (s) solid, (l) liquid, (g) gas, (aq) aqueous solution. For example: 2Mg(s) + O₂(g) → 2MgO(s).
配平过程是在分子式前面添加大数字（系数）。状态符号写在括号中：(s) 固体, (l) 液体, (g) 气体, (aq) 水溶液。例如：2Mg(s) + O₂(g) → 2MgO(s)。
5. Types of Chemical Reactions and General Equations | 化学反应类型与通式
Many reactions in Year 9 fall into recognisable patterns. A combination reaction joins two or more substances to form a single product: A + B → AB. A decomposition reaction breaks a compound into simpler substances: AB → A + B.
Year 9 阶段的许多反应都属于可识别的类型。化合反应是将两种或多种物质结合成一种产物：A + B → AB。分解反应是将化合物分解为更简单的物质：AB → A + B。
Combustion is the reaction of a substance with oxygen, producing oxides and energy. For hydrocarbons, the general equation for complete combustion is: CₓHᵧ + (x + y/4) O₂ → xCO₂ + (y/2)H₂O. Incomplete combustion gives CO or C as soot.
燃烧是物质与氧气发生的反应，生成氧化物并释放能量。对于碳氢化合物，完全燃烧的通式为：CₓHᵧ + (x + y/4) O₂ → xCO₂ + (y/2)H₂O。不完全燃烧则生成 CO 或碳黑。
Displacement reactions occur when a more reactive element pushes a less reactive one out of its compound. The general form is: A + BC → AC + B, where A is more reactive than B.
置换反应发生在较活泼的元素将较不活泼的元素从其化合物中置换出来时。通式为：A + BC → AC + B，其中 A 比 B 更活泼。
6. The Reactivity Series and Displacement Reactions | 金属活动性顺序与置换反应
The reactivity series lists metals in order of their willingness to lose electrons and form positive ions. A common mnemonic from most to least reactive: Potassium, Sodium, Calcium, Magnesium, Aluminium, (Carbon), Zinc, Iron, (Hydrogen), Copper, Silver, Gold. Carbon and hydrogen are included as reference points for extraction and acid reactions.
金属活动性顺序将金属按照失电子形成阳离子的倾向排列。从最活泼到最不活泼的常见记忆顺序为：钾、钠、钙、镁、铝、(碳)、锌、铁、(氢)、铜、银、金。碳和氢被包括在内，分别作为冶炼和酸反应的参照点。
A metal will displace a less reactive metal from a solution of its salt. For example: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s). No reaction occurs if the free metal is lower in the reactivity series than the metal in the compound.
一种金属能将比它不活泼的金属从其盐溶液中置换出来。例如：Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)。若单质金属的活动性低于化合物中的金属，则不会发生反应。
7. Acids, Bases, Salts and Neutralisation | 酸、碱、盐和中和反应
An acid is a substance that produces hydrogen ions (H⁺) when dissolved in water. Common laboratory acids are HCl, H₂SO₄ and HNO₃. A base is a substance that can neutralise an acid; an alkali is a soluble base that produces hydroxide ions (OH⁻) in water.
酸是溶于水时产生氢离子 (H⁺) 的物质。实验室常见的酸有盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。碱是能中和酸的物质；可溶性的碱称为碱液，它在水中产生氢氧根离子 (OH⁻)。
Neutralisation: Acid + Base → Salt + Water
中和反应：酸 + 碱 → 盐 + 水
The ionic equation for neutralisation between a strong acid and a strong alkali is always: H⁺(aq) + OH⁻(aq) → H₂O(l). Reactions of acids with metals produce a salt and hydrogen gas: Metal + Acid → Salt + Hydrogen. Acids with carbonates give salt, water and carbon dioxide.
强酸和强碱中和的离子方程式总是：H⁺(aq) + OH⁻(aq) → H₂O(l)。酸与金属反应生成盐和氢气：金属 + 酸 → 盐 + 氢气。酸与碳酸盐反应则生成盐、水和二氧化碳。
8. Principles of Electrolysis | 电解的基本原理
Electrolysis is the decomposition of an ionic compound, either molten or in aqueous solution, using a direct electric current. Positive ions (cations) migrate to the negative electrode (cathode) and gain electrons (reduction). Negative ions (anions) move to the positive electrode (anode) and lose electrons (oxidation).
电解是利用直流电使离子化合物（熔融态或水溶液）分解的过程。阳离子（正离子）移向负极（阴极）并获得电子（还原反应）。阴离子（负离子）移向正极（阳极）并失去电子（氧化反应）。
For a molten salt such as lead(II) bromide: Pb²⁺ + 2e⁻ → Pb (at cathode); 2Br⁻ → Br₂ + 2e⁻ (at anode). In aqueous solutions, the products depend on the relative ease of discharge. For example, at the cathode, hydrogen is produced if the metal is more reactive than hydrogen; otherwise the metal plates out.
对于像熔融溴化铅这样的盐：Pb²⁺ + 2e⁻ → Pb（阴极）; 2Br⁻ → Br₂ + 2e⁻（阳极）。在水溶液中，电解产物取决于离子的放电顺序。例如在阴极，若金属比氢活泼则析出氢气，否则金属会析出。
9. Rate of Reaction and Factors Affecting It | 反应速率及其影响因素
The rate of a chemical reaction is a measure of how quickly reactants are used up or products are formed. It can be expressed as: Rate = change in amount (or concentration) / time taken. Common units are mol/dm³/s or g/s.
化学反应速率是衡量反应物消耗或产物生成快慢的物理量。可表示为：速率 = 某种物质的量（或浓度）的变化 / 所需时间。常用单位有 mol/dm³/s 或 g/s。
Four main factors increase the rate: higher temperature, higher concentration (or pressure for gases), smaller particle size (greater surface area), and the presence of a catalyst. All are explained by collision theory: particles must collide with sufficient energy (activation energy) and correct orientation.
四种主要因素可加快反应速率：升高温度、增大浓度（或气体的压强）、减小固体颗粒尺寸（增大表面积）和使用催化剂。这些都可以用碰撞理论解释：粒子必须发生有效碰撞，即具有足够能量（活化能）且取向合适。
10. Principles of Separation and Purification Techniques | 分离与纯化技术原理
Mixtures can be separated by physical methods that exploit differences in a particular property. Filtration separates an insoluble solid from a liquid using filter paper; the solid remains as residue, the liquid passes through as filtrate.
混合物可通过基于某种性质差异的物理方法分离。过滤利用滤纸将不溶性固体和液体分开；固体留在滤纸上成为残渣，液体透过滤纸成为滤液。
Evaporation is used to obtain a soluble solid from a solution by heating until the solvent boils off. Crystallisation gives pure solid crystals by gently evaporating solvent until crystallisation point, then cooling.
蒸发是通过加热使溶剂沸腾除去，从而从溶液中获得可溶性固体。结晶法则是通过缓慢蒸发溶剂至结晶点，再冷却以得到纯净的固体晶体。
Simple distillation separates a liquid from a solution (or from a liquid mixture with a large boiling-point difference) by boiling and condensing the vapour. Fractional distillation separates two or more miscible liquids with close boiling points using a fractionating column. Chromatography separates small quantities of dissolved substances based on their differing affinities for a stationary phase and a mobile phase.
简单蒸馏通过加热沸腾再将蒸气冷凝，可将液体从溶液中分离（或分离沸点相差较大的液态混合物）。分馏则借助分馏柱，分离沸点相近的两种或多种互溶液体。色谱法利用溶质在固定相和流动相中亲和力的不同，分离微量溶解物质。
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