📚 Year 8 WJEC Chemistry: Formula & Theorem Quick Reference Handbook | Year 8 WJEC 化学：公式定理速查手册
This quick reference handbook brings together all the essential formulas, rules and key principles you will meet in Year 8 WJEC Chemistry. Keep it handy for homework, tests and end-of-year revision – every topic from atoms to reactions is covered in a clear, paired English–Chinese format.
这本速查手册汇集了八年级 WJEC 化学课程中所有关键的公式、规则和核心原理。无论是做作业、准备测验还是期末复习，你都可以随时查阅——从原子到化学反应，每个主题都以清晰的中英对照方式呈现。
1. Chemical Symbols and Writing Formulae | 化学符号与化学式的书写
Every element has a unique chemical symbol, consisting of one or two letters. The first letter is always capitalised, and the second, if present, is lowercase. For example, carbon is C, sodium is Na and oxygen is O.
每种元素都有独特的化学符号，由一个或两个字母组成。第一个字母必须大写，如果有第二个字母则小写。例如，碳是 C，钠是 Na，氧是 O。
When elements combine, we write chemical formulae using the symbols and small subscript numbers to show how many atoms of each element are present. No subscript means one atom. For instance, water is H₂O, carbon dioxide is CO₂ and methane is CH₄.
当元素化合时，我们用元素符号和小的下标数字来表示每种原子的数目，这就是化学式。没有下标数字表示 1 个原子。例如水是 H₂O，二氧化碳是 CO₂，甲烷是 CH₄。
For compounds containing groups of atoms that stay together, we use brackets. Calcium hydroxide is Ca(OH)₂, meaning one calcium atom and two hydroxide (OH) groups.
对于含有原子团的化合物，我们需要使用括号。例如氢氧化钙的化学式是 Ca(OH)₂，表示一个钙原子和两个氢氧根 (OH)。
2. Balancing Equations: The Law of Conservation of Mass | 配平方程式：质量守恒定律
In a chemical reaction, atoms are rearranged but never created or destroyed. This is the law of conservation of mass: the total mass of reactants equals the total mass of products.
在化学反应中，原子重新排列，但既不会被创造也不会被消灭。这就是质量守恒定律：反应物的总质量等于生成物的总质量。
A symbol equation must be balanced so that the number of each type of atom is the same on both sides. You balance by placing large numbers (coefficients) in front of the symbols or formulae. You must never change the small subscript numbers inside a formula.
化学符号方程式必须配平，使每种原子的数目在左右两边相等。配平时，在化学式前面添加大的系数（整数），绝不能改动化学式内的小下标数字。
Example: H₂ + O₂ → 2H₂O. Two molecules of hydrogen react with one molecule of oxygen to give two molecules of water. Check: 4 H atoms and 2 O atoms on each side.
示例：H₂ + O₂ → 2H₂O。两个氢分子与一个氧分子反应，生成两个水分子。检查：两边各有 4 个氢原子和 2 个氧原子。
3. 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 1/12 of the mass of a carbon‑12 atom. It has no units.
元素的相对原子质量 (Ar) 是其原子的平均质量与一个碳‑12 原子质量的 1/12 的比值，没有单位。
The Ar tells us how heavy an atom is relative to another. For example, Ar of oxygen is 16, meaning one oxygen atom is 16 times heavier than 1/12 of a carbon‑12 atom.
Ar 告诉我们一个原子相对于另一个原子的质量。例如，氧的 Ar 为 16，表示一个氧原子的质量是碳‑12 原子质量的 1/12 的 16 倍。
You can find Ar values on the periodic table. In Year 8, we round Ar to the nearest whole number for simple calculations. So sodium (Na) has Ar = 23, and chlorine (Cl) has Ar = 35.5.
你可以在元素周期表上找到 Ar 值。在八年级，我们通常将 Ar 取整以进行简单计算。例如钠 (Na) 的 Ar ≈ 23，氯 (Cl) 的 Ar ≈ 35.5。
4. Calculating Reacting Masses | 反应质量计算
The conservation of mass allows us to predict the mass of a product or reactant if we know the balanced equation and the mass of one substance. We use the formula masses and the ratio from the equation.
利用质量守恒定律，如果我们知道配平的化学方程式和一种物质的质量，就可以预测产物或反应物的质量。计算时要利用化学式量和方程式中的比例。
Step‑by‑step method: (1) Write the balanced equation. (2) Work out the relative formula mass (Mr) for each substance using Ar values. (3) Use the ratio from the equation to scale the masses.
计算步骤：(1) 写出配平的化学方程式。(2) 用 Ar 值计算每种物质的相对化学式量 (Mr)。(3) 利用方程式中的系数比例来计算质量。
Example: 2Mg + O₂ → 2MgO. If 48 g of magnesium burns completely, what mass of magnesium oxide forms? Ar(Mg)=24, Mr(MgO)=24+16=40. From the equation, 2×24 g Mg gives 2×40 g MgO, so 48 g Mg gives 80 g MgO.
示例：2Mg + O₂ → 2MgO。如果 48 g 镁完全燃烧，生成多少克氧化镁？Ar(Mg)=24，Mr(MgO)=24+16=40。由方程式可知，2×24 g Mg 生成 2×40 g MgO，所以 48 g Mg 生成 80 g MgO。
5. Concentration of Solutions | 溶液浓度
The concentration of a solution tells us how much solute is dissolved in a certain volume of solvent. In Year 8 we usually measure concentration in grams per cubic decimetre (g/dm³). A cubic decimetre is the same as a litre (1 dm³ = 1000 cm³).
溶液的浓度表示在一定体积的溶剂中溶解了多少溶质。八年级通常用克每立方分米 (g/dm³) 来表示浓度。1 立方分米等于 1 升 (1 dm³ = 1000 cm³)。
The formula is:
Concentration (g/dm³) = mass of solute (g) ÷ volume (dm³)
公式为：
浓度 (g/dm³) = 溶质质量 (g) ÷ 溶液体积 (dm³)
If 20 g of salt is dissolved in water to make 0.5 dm³ of solution, the concentration is 20 ÷ 0.5 = 40 g/dm³. Always convert cm³ to dm³ by dividing by 1000 before using the formula.
如果将 20 g 盐溶于水配成 0.5 dm³ 溶液，浓度就是 20 ÷ 0.5 = 40 g/dm³。使用公式前，一定要先把 cm³ 除以 1000 转化为 dm³。
6. The pH Scale and Neutralisation | pH 标度与中和反应
The pH scale runs from 0 to 14 and measures how acidic or alkaline a solution is. Acids have a pH less than 7, pure water is neutral at pH 7, and alkalis have a pH greater than 7. Universal indicator changes colour across the range.
pH 范围从 0 到 14，用于衡量溶液的酸碱度。酸的 pH 小于 7，纯水中性为 pH 7，碱的 pH 大于 7。通用指示剂在不同 pH 会显示出不同的颜色。
Neutralisation occurs when an acid and a base (or alkali) react together to form a salt and water. The general word equation is:
Acid + Base → Salt + Water
中和反应是酸和碱（或 alkali）反应生成盐和水的过程。一般文字方程式为：
酸 + 碱 → 盐 + 水
During neutralisation, the H⁺ ions from the acid and the OH⁻ ions from the alkali join to make H₂O molecules. The pH moves towards 7 as the reaction proceeds.
中和过程中，酸中的 H⁺ 离子与碱中的 OH⁻ 离子结合生成 H₂O 分子。随着反应的进行，pH 逐渐趋向 7。
7. Acids, Bases and Naming Salts | 酸、碱与盐的命名
Common laboratory acids are hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Alkalis include sodium hydroxide (NaOH) and potassium hydroxide (KOH). Metal oxides and hydroxides act as bases.
实验室常见的酸有盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。常见的碱有氢氧化钠 (NaOH) 和氢氧化钾 (KOH)。金属氧化物和氢氧化物也属于碱。
The name of the salt formed depends on the acid and the metal or base used. The first part comes from the metal, and the second part comes from the acid:
生成的盐的名称取决于所用的酸和金属（或碱）。名称的前半部分来自金属，后半部分来自酸根：
| Acid | Salt ending | Example |
|---|---|---|
| Hydrochloric acid | … chloride | Sodium chloride (NaCl) |
| Sulfuric acid | … sulfate | Copper sulfate (CuSO₄) |
| Nitric acid | … nitrate | Potassium nitrate (KNO₃) |
When naming the salt, the metal always comes first. For transition metals that can form different ions, Roman numerals indicate the charge, but this is only needed if the metal has more than one possible ion.
命名盐时，金属部分总是放在前面。对于能够形成不同离子的过渡金属，需要用罗马数字标明电荷，不过只有当金属可能有多种离子时才需要这样做。
8. States of Matter and Kinetic Theory | 物质状态与分子运动理论
All substances exist as solids, liquids or gases depending on temperature and pressure. Kinetic theory explains the behaviour of particles in each state. In solids, particles are held in fixed positions and vibrate. In liquids, particles are close together but can move past each other. In gases, particles are far apart and move rapidly in all directions.
所有物质都以固态、液态或气态存在，这取决于温度和压力。分子运动理论解释了每种状态下粒子的行为。固体中，粒子固定在位置上振动；液体中，粒子紧紧靠在一起但可以相对滑动；气体中，粒子相距很远并快速地向各个方向运动。
Changes of state are physical changes, not chemical ones. Melting, freezing, boiling, evaporation and condensation all involve energy transfer without making new substances. The melting point and boiling point are characteristic properties of a pure substance.
状态变化是物理变化，而不是化学变化。熔化、凝固、沸腾、蒸发和凝结都只涉及能量转移，不会生成新物质。熔点和沸点是纯净物的特征性质。
Diffusion in liquids and gases provides evidence for the kinetic particle model. Heavier particles move more slowly than lighter ones at the same temperature.
液体和气体中的扩散现象为粒子运动模型提供了证据。在相同温度下，较重的粒子比较轻的粒子运动得更慢。
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. A common Year 8 series is: potassium (most reactive), sodium, calcium, magnesium, aluminium, zinc, iron, copper, silver, gold (least reactive). Carbon is often included as a reference for metal extraction.
金属活动性顺序根据金属反应的剧烈程度排列。八年级常用的顺序为：钾（最活泼）、钠、钙、镁、铝、锌、铁、铜、银、金（最不活泼）。碳也常被包括在内，作为冶炼金属的参照。
A more reactive metal will displace a less reactive metal from its compound. For example, placing magnesium in copper sulfate solution: Mg + CuSO₄ → MgSO₄ + Cu. The blue colour of the copper sulfate fades as copper metal coats the magnesium.
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。例如，将镁放入硫酸铜溶液中：Mg + CuSO₄ → MgSO₄ + Cu。硫酸铜的蓝色逐渐褪去，镁条表面覆盖上一层铜。
The reactivity series also helps predict reactions with water and acids. Potassium, sodium and calcium react vigorously with cold water; magnesium reacts slowly with water but well with acid; copper and gold do not react with dilute acids.
利用活动性顺序还可以预测金属与水和酸的反应。钾、钠、钙与冷水剧烈反应；镁与冷水反应缓慢但能与酸迅速反应；铜和金则不与稀酸反应。
10. Separation Techniques | 分离方法
Mixtures can be separated using physical methods that exploit differences in properties like boiling point, solubility and particle size. Key techniques for Year 8 WJEC include:
混合物可以利用物理方法进行分离，这些方法依据的是沸点、溶解度、颗粒大小等性质的不同。八年级 WJEC 的关键分离技术包括：
Filtration: separates an insoluble solid from a liquid using filter paper. The solid stays as residue, the liquid passes through as filtrate. Example: sand from water.
过滤：用滤纸将不溶性固体与液体分开。固体留在滤纸上成为残渣，液体穿过滤纸成为滤液。实例：将沙子从水中分离出来。
Evaporation and crystallisation: used to obtain a soluble solid from a solution. Heat the solution to evaporate the solvent, leaving the solid behind. Slow cooling forms crystals.
蒸发与结晶：用于从溶液中获得可溶性固体。加热溶液使溶剂蒸发，留下固体。缓慢冷却可以生成晶体。
Simple distillation: separates a solvent from a solution by boiling and then condensing the vapour. The pure liquid (distillate) is collected. It works because the solvent has a much lower boiling point than the solute.
简单蒸馏：通过加热使溶剂沸腾，然后将蒸气冷凝，从而将溶剂从溶液中分离出来。收集到的纯液体称为馏出液。该方法可行的原因是溶剂的沸点远低于溶质。
Chromatography: separates mixtures of coloured substances by their different solubilities in a solvent. A baseline is drawn in pencil, spots are placed, and the paper is dipped in solvent. The more soluble a substance travels further up the paper.
色谱法：利用不同物质在溶剂中溶解度的差异来分离混合物。用铅笔画基线，点上试样，然后将滤纸末端浸入溶剂。溶解度越大的物质在纸上爬升得越远。
11. Rates of Reaction and Collision Theory | 反应速率与碰撞理论
The rate of a chemical reaction tells us how quickly reactants are used up or products are made. Collision theory states that for a reaction to occur, particles must collide with enough energy (activation energy) and in the correct orientation.
化学反应速率表示反应物被消耗或产物生成的速度。碰撞理论指出，要发生反应，粒子必须以足够的能量（活化能）和正确的朝向发生碰撞。
Factors that increase the frequency of successful collisions increase the rate. These are:
增加成功碰撞频率的因素会加快反应速率，这些因素包括：
Temperature: heating gives particles more kinetic energy, so they move faster and collide more often and with more energy.
温度：加热使粒子获得更多动能，运动更快，碰撞更频繁且能量更高。
Concentration (or pressure for gases): more particles in the same volume means a greater chance of collision.
浓度（或气体压强）：相同体积内粒子越多，碰撞机会越大。
Surface area: breaking a solid into smaller pieces exposes more particles to collide with reactants. Powdered chalk reacts faster with acid than a large lump.
表面积：将固体粉碎成小块可以让更多粒子暴露并与其他反应物碰撞。粉末状的白垩与酸的反应比大块白垩快得多。
Catalysts: substances that speed up a reaction without being used up themselves. They provide an alternative pathway with a lower activation energy.
催化剂：能加快反应速率而自身不被消耗的物质。催化剂通过提供一条活化能更低的反应路径来起作用。
12. Key Word Glossary & Formula Summary | 关键词汇与公式汇总
Use this final section to quickly check definitions and core mathematical relationships. All terms are matched to their WJEC Year 8 context.
你可以用最后这一节快速查阅定义和核心数学关系。所有术语都与 WJEC 八年级课程内容匹配。
| English term | 中文术语 | Brief definition / 简要定义 |
|---|---|---|
| Atom | 原子 | Smallest particle of an element that can take part in a chemical reaction / 能参与化学反应的元素最小粒子 |
| Molecule | 分子 | Two or more atoms chemically bonded together / 两个或以上原子通过化学键结合 |
| Compound | 化合物 | Substance made from two or more different elements chemically joined / 由两种或以上不同元素化合而成的物质 |
| Ion | 离子 | Charged particle formed when an atom gains or loses electrons / 原子得失电子后形成的带电粒子 |
| Mr (Relative formula mass) | 相对化学式量 | Sum of Ar values of all atoms in a formula / 化学式中所有原子的 Ar 之和 |
| Concentration (g/dm³) | 浓度 | Mass of solute per unit volume of solution / 单位体积溶液中溶质的质量 |
The key equation to remember: Concentration = mass ÷ volume (in dm³). Also, the total mass before and after a reaction remains constant – the law of conservation of mass is the foundation of all stoichiometry.
需要牢记的关键公式：浓度 = 质量 ÷ 体积（dm³）。此外，反应前后总质量保持不变——质量守恒定律是所有化学计量计算的基础。
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply