📚 Year 9 CCEA Chemistry: Quick Reference Formulas & Theorems | 九年级CCEA化学：公式定理速查手册
This handbook provides an at‑a‑glance summary of the essential formulas, definitions, and principles you need for Year 9 CCEA Chemistry. Use it to review atomic structure, chemical reactions, quantitative chemistry, acids and bases, and reaction rates – all in one place.
本手册为你提供九年级CCEA化学所需的核心公式、定义和原理的速查汇总，涵盖原子结构、化学反应、定量化学、酸碱以及反应速率等重点内容，方便随时翻阅复习。
1. Law of Conservation of Mass | 质量守恒定律
In a chemical reaction, mass is neither created nor destroyed. The total mass of the reactants is always equal to the total mass of the products.
在化学反应中，质量既不会凭空创生，也不会凭空消灭。反应物的总质量总是等于生成物的总质量。
If 10.0 g of calcium carbonate (CaCO₃) decomposes completely, the sum of the masses of calcium oxide (CaO) and carbon dioxide (CO₂) produced will still be 10.0 g.
如果 10.0 克碳酸钙 (CaCO₃) 完全分解，生成的氧化钙 (CaO) 和二氧化碳 (CO₂) 的质量总和仍为 10.0 克。
mass of reactants = mass of products
2. Relative Atomic Mass (Ar) | 相对原子质量 (Ar)
The relative atomic mass (Ar) of an element is the average mass of its atoms compared to 1/12th of the mass of a carbon‑12 atom. It has no unit.
元素的相对原子质量 (Ar) 是其所有同位素原子的平均质量与一个碳‑12 原子质量的 1/12 相比较的比值，没有单位。
Common Ar values: hydrogen ≈ 1, carbon ≈ 12, oxygen ≈ 16, sodium ≈ 23, chlorine ≈ 35.5.
常见 Ar 值：氢 ≈ 1，碳 ≈ 12，氧 ≈ 16，钠 ≈ 23，氯 ≈ 35.5。
Ar = (average mass of one atom) / (1/12 × mass of one ¹²C atom)
3. Relative Molecular Mass (Mr) | 相对分子质量 (Mr)
The relative molecular mass (Mr) of a compound is the sum of the relative atomic masses of all the atoms in its formula. Like Ar, it has no unit.
化合物的相对分子质量 (Mr) 等于它化学式中所有原子的相对原子质量之和。与 Ar 一样，它也没有单位。
For water (H₂O): Mr = 2 × Ar(H) + 1 × Ar(O) = 2×1 + 16 = 18.
对于水 (H₂O)：Mr = 2 × Ar(H) + 1 × Ar(O) = 2×1 + 16 = 18。
Mr = Σ (Ar of each element × number of atoms of that element)
4. Percentage Composition by Mass | 质量百分比组成
Percentage composition tells you the mass percentage of each element in a compound. It is calculated using the total mass of the element in one formula unit divided by the Mr, multiplied by 100%.
质量百分比组成表示化合物中每种元素所占的质量百分比。用该元素在化学式中的总质量除以化合物的 Mr，再乘以 100% 即可求得。
In H₂O: % H = (2×1 / 18) × 100% ≈ 11.1%; % O = (16 / 18) × 100% ≈ 88.9%.
在水 (H₂O) 中：H 的质量百分比 = (2×1/18) × 100% ≈ 11.1%；O 的质量百分比 = (16/18) × 100% ≈ 88.9%。
% element = (total Ar of element in formula / Mr of compound) × 100%
5. Writing Chemical Formulae | 化学式的书写
Chemical formulae use element symbols and subscript numbers to show the types and ratios of atoms. For ionic compounds, the positive and negative charges must balance.
化学式用元素符号和下标数字表示原子的种类与个数比。离子化合物的化学式中，正负电荷总数必须相等。
Using ion charges: sodium ion Na⁺ and chloride ion Cl⁻ give NaCl; aluminium ion Al³⁺ and oxide ion O²⁻ give Al₂O₃.
利用离子电荷书写：钠离子 Na⁺ 与氯离子 Cl⁻ 组成 NaCl；铝离子 Al³⁺ 与氧离子 O²⁻ 组成 Al₂O₃。
For covalent molecules, the subscript shows the number of each atom directly: H₂O, CO₂, NH₃.
对于共价分子，下标直接表示各原子的数目：H₂O、CO₂、NH₃。
6. 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. Coefficients (big numbers in front) are added to achieve this without changing the chemical formulae.
配平的化学方程式两边每种原子的数目相等。通过添加化学计量数（物质前面的系数）来实现配平，而不改变化学式本身。
+ O₂ → H₂O. Count atoms: 2H + 2O → 2H + 1O. Balanced: 2H₂ + O₂ → 2H₂O (4H + 2O → 4H + 2O).
未配平：H₂ + O₂ → H₂O。计算原子数：2H + 2O → 2H + 1O。配平后：2H₂ + O₂ → 2H₂O（4H + 2O → 4H + 2O）。
Step 1: list atoms; Step 2: adjust coefficients; Step 3: check all atoms.
7. Reactivity Series of Metals | 金属活动性顺序
The reactivity series ranks metals by how readily they react. More reactive metals can displace less reactive metals from their compounds.
金属活动性顺序根据金属反应的难易程度排列。位于前面的活泼金属能把位于后面的较不活泼金属从其化合物中置换出来。
Common order: K > Na > Ca > Mg > Al > Zn > Fe > Sn > Pb > (H) > Cu > Hg > Ag > Pt > Au.
常见顺序：钾 > 钠 > 钙 > 镁 > 铝 > 锌 > 铁 > 锡 > 铅 > (氢) > 铜 > 汞 > 银 > 铂 > 金。
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s). Zinc displaces copper because it is more reactive.
示例：Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)。锌比铜活泼，因此置换出铜。
8. Reactions of Metals with Acids | 金属与酸的反应
lt and hydrogen gas are produced. The general equation is: metal + acid → salt + hydrogen.
金属与酸反应生成盐和氢气。一般表示式为：金属 + 酸 → 盐 + 氢气。
xample: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g). The hydrogen can be tested with a lit splint – it burns with a squeaky pop.
示例：Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)。生成的氢气可用燃着的木条检验——氢气燃烧发出爆鸣声。
metal + acid → salt + H₂
9. Neutralisation Reaction | 中和反应
Neutralisation occurs when an acid and a base (or alkali) react to form a salt and water. The H⁺ ions from the acid combine with OH⁻ ions to produce H₂O.
酸和碱（或可溶碱）发生中和反应，生成盐和水。酸中的 H⁺ 离子与碱中的 OH⁻ 离子结合生成 H₂O。
Word equation: hydrochloric acid + sodium hydroxide → sodium chloride + water.
文字表达式：盐酸 + 氢氧化钠 → 氯化钠 + 水。
H⁺(aq) + OH⁻(aq) → H₂O(l)
10. The pH Scale | pH 标度
The pH scale (0‑14) measures the acidity or alkalinity of a solution. Acids have a pH less than 7, neutral solutions have pH 7, and alkalis have a pH greater than 7.
pH 标度 (0‑14) 用来衡量溶液的酸碱性。酸性溶液的 pH < 7，中性溶液 pH = 7，碱性溶液的 pH > 7。
Common indicators: litmus turns red in acid and blue in alkali; universal indicator shows a range of colours (red/orange for acid, green for neutral, blue/purple for alkali).
常用指示剂：石蕊遇酸变红、遇碱变蓝；通用指示剂呈现一系列颜色（酸为红/橙，中性为绿，碱为蓝/紫）。
pH = -log₁₀[H⁺] (simpler version for Year 9: low pH = high acidity)
11. States of Matter & Particle Theory | 物质状态与粒子理论
All matter is made of tiny particles. The arrangement and movement of these particles determine whether a substance is a solid, liquid, or gas.
所有物质都由微小粒子构成。粒子的排列方式和运动状态决定了物质是固体、液体还是气体。
In solids, particles are tightly packed in a regular pattern and vibrate in fixed positions. In liquids, particles are close together but can move past each other. In gases, particles are far apart and move rapidly in all directions.
固体中，粒子紧密、有规律地排列，只能在固定位置振动；液体中，粒子紧密但能相互滑过；气体中，粒子彼此远离，快速向各个方向运动。
Changes of state – melting, freezing, boiling, condensing, sublimation – involve energy transfer but no change in particle identity.
状态变化（熔化、凝固、沸腾、冷凝、升华）涉及能量转移，但粒子本身的种类不发生改变。
12. Factors Affecting the Rate of Reaction | 影响反应速率的因素
The rate of a chemical reaction can be altered by changing temperature, concentration, surface area of solid reactants, or by adding a catalyst.
改变温度、反应物浓度、固体反应物的表面积或加入催化剂，都可以改变化学反应的速率。
Increasing temperature speeds up reactions because particles have more kinetic energy, collide more often, and have more successful collisions.
升高温度会加快反应速率，因为粒子动能增大，碰撞更频繁，有效碰撞次数更多。
Increasing concentration or surface area also increases collision frequency. A catalyst provides an alternative pathway with lower activation energy, speeding up the reaction without being used up.
增大浓度或增加固体表面积也能提高碰撞频率。催化剂则通过提供较低活化能的反应途径来加快反应，且自身在反应中不会被消耗。
rate ∝ collision frequency × fraction of successful collisions
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