📚 Year 8 Edexcel Chemistry: Formula & Theorem Quick Reference Guide | Year 8 Edexcel 化学：公式定理速查手册
This concise handbook brings together all the essential formulas, equations and key theorems you will encounter in Year 8 Edexcel Chemistry. Use it for rapid revision, homework support and exam preparation.
这本简明手册汇集了 Year 8 Edexcel 化学中你会遇到的所有核心公式、方程式和重要定理。可用作快速复习、作业辅助和备考资料。
1. Law of Conservation of Mass | 质量守恒定律
During any chemical reaction, the total mass of the reactants is always equal to the total mass of the products. Atoms are neither created nor destroyed; they are only rearranged.
在任何化学反应中，反应物的总质量总是等于生成物的总质量。原子既不会凭空消失也不会凭空产生，只是重新组合。
Total mass of reactants = Total mass of products
This law is the reason why we must balance chemical equations. If an equation is not balanced, the number of atoms of each element will not be the same on both sides, which would violate the law.
这一定律是我们必须配平化学方程式的原因。如果方程式没有配平，两边各元素的原子数就不相等，这就违背了质量守恒定律。
Example: When magnesium burns in oxygen, the mass of magnesium oxide produced equals the combined mass of magnesium and oxygen that reacted.
示例：镁在氧气中燃烧时，生成的氧化镁的质量等于参加反应的镁和氧气的质量之和。
2. Relative Atomic Mass and Formula Mass | 相对原子质量与式量
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. You can find Ar values from the periodic table.
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 相比较的数值。Ar 数值可从元素周期表中查到。
The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of all the atoms in its formula.
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。
Mr = Σ Ar (of each atom in the formula)
Worked example – water (H₂O): Ar of H = 1, Ar of O = 16. Therefore Mr(H₂O) = (2 × 1) + 16 = 18.
计算示例——水 (H₂O)：H 的 Ar = 1, O 的 Ar = 16。因此 Mr(H₂O) = (2 × 1) + 16 = 18。
For ionic compounds such as sodium chloride (NaCl), Mr = 23 + 35.5 = 58.5.
对于氯化钠 (NaCl) 等离子化合物，Mr = 23 + 35.5 = 58.5。
3. Writing and Balancing Chemical Equations | 化学方程式的书写与配平
A balanced chemical equation shows the correct ratio of reactants and products, with equal numbers of each type of atom on both sides.
配平的化学方程式以正确的比例表示反应物和生成物，并且两边各元素的原子数是相等的。
Steps to balance an equation:
- Write the correct chemical formula for each reactant and product.
- Count the number of atoms of each element on both sides.
- Place large numbers (coefficients) in front of the formulas to balance the atoms.
- Check that all coefficients are in the simplest whole-number ratio.
配平方程式的步骤：
- 写出每种反应物和生成物的正确化学式。
- 数清两边各元素的原子个数。
- 在化学式前面放置整数（系数）使原子数相等。
- 检查所有系数是否为最简整数比。
Example: H₂ + Cl₂ → 2HCl (hydrogen and chlorine react to form hydrogen chloride).
示例：H₂ + Cl₂ → 2HCl（氢气和氯气反应生成氯化氢）。
Another example: 2Mg + O₂ → 2MgO (magnesium burns in oxygen).
另一示例：2Mg + O₂ → 2MgO（镁在氧气中燃烧）。
4. Valency and Chemical Formulae | 化合价与化学式
Valency is the combining power of an element or ion. Using valencies correctly helps us write the correct formula of a compound.
化合价是元素或离子的结合能力。正确使用化合价有助于我们书写化合物的正确化学式。
Common valencies and ions:
| Ion / Group | Charge |
|---|---|
| Na⁺, K⁺, Ag⁺ | 1+ |
| Mg²⁺, Ca²⁺, Cu²⁺, Fe²⁺ | 2+ |
| Al³⁺, Fe³⁺ | 3+ |
| Cl⁻, Br⁻, I⁻, OH⁻ | 1– |
| O²⁻, S²⁻, SO₄²⁻, CO₃²⁻ | 2– |
| NO₃⁻ | 1– |
| NH₄⁺ | 1+ |
To write a formula, swap the charges of the positive and negative ions and write them as subscripts, then simplify the ratio if possible. For example, Al³⁺ and O²⁻ combine to form Al₂O₃.
书写化学式时，将正、负离子的电荷数互换并写成下标，然后尽可能简化比例。例如 Al³⁺ 与 O²⁻ 结合形成 Al₂O₃。
Never change the charges when writing the formula – only use the crossover method.
书写化学式时不要更改电荷，只需使用交叉法即可。
5. Reactions of Metals with Acids | 金属与酸的反应
When a metal reacts with an acid, a salt and hydrogen gas are produced. The general word equation is:
当金属与酸反应时，会生成一种盐和氢气。通用文字方程式为：
Metal + Acid → Salt + Hydrogen (H₂)
Example: Zinc + Hydrochloric acid → Zinc chloride + Hydrogen
示例：锌 + 盐酸 → 氯化锌 + 氢气
The salt produced depends on the metal and the acid used: hydrochloric acid gives chlorides, sulfuric acid gives sulfates, and nitric acid gives nitrates.
生成的盐取决于所用的金属和酸：盐酸生成氯化物，硫酸生成硫酸盐，硝酸生成硝酸盐。
Not all metals react with acids; copper, for instance, does not react with dilute hydrochloric acid because it is less reactive than hydrogen. The reactivity series can help predict whether a reaction will occur.
并非所有金属都能与酸反应；例如铜不与稀盐酸反应，因为其活泼性低于氢。金属活动性顺序可帮助预测反应是否发生。
6. Neutralisation Reactions | 中和反应
Neutralisation is the reaction between an acid and a base (or alkali) to produce a salt and water. It is a very important type of reaction in chemistry.
中和反应是酸与碱（或碱性物质）反应生成盐和水的过程。这是化学中非常重要的一类反应。
Acid + Alkali → Salt + Water
Other common neutralisation patterns:
- Acid + Metal oxide → Salt + Water
- Acid + Metal carbonate → Salt + Water + Carbon dioxide
其他常见中和反应模式：
- 酸 + 金属氧化物 → 盐 + 水
- 酸 + 碳酸盐 → 盐 + 水 + 二氧化碳
Examples: Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water (HCl + NaOH → NaCl + H₂O). Sulfuric acid + Copper oxide → Copper sulfate + Water. Hydrochloric acid + Calcium carbonate → Calcium chloride + Water + Carbon dioxide.
示例：盐酸 + 氢氧化钠 → 氯化钠 + 水 (HCl + NaOH → NaCl + H₂O)。硫酸 + 氧化铜 → 硫酸铜 + 水。盐酸 + 碳酸钙 → 氯化钙 + 水 + 二氧化碳。
7. Combustion Reactions | 燃烧反应
Combustion is the reaction of a fuel with oxygen that releases heat and light. When a hydrocarbon burns in a plentiful supply of oxygen (complete combustion), the products are carbon dioxide and water.
燃烧是燃料与氧气发生反应并释放热量和光的过程。当碳氢化合物在充足的氧气中燃烧（完全燃烧）时，产物是二氧化碳和水。
Hydrocarbon + O₂ → CO₂ + H₂O
Example – methane (natural gas): CH₄ + 2O₂ → CO₂ + 2H₂O
示例——甲烷（天然气）：CH₄ + 2O₂ → CO₂ + 2H₂O
Example – propane: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
示例——丙烷：C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
If the oxygen supply is limited (incomplete combustion), carbon monoxide (CO) or soot (carbon) may be produced instead. Incomplete combustion is dangerous because carbon monoxide is a toxic gas.
如果氧气供应不足（不完全燃烧），则可能生成一氧化碳 (CO) 或碳（烟灰）。不完全燃烧具有危险性，因为一氧化碳是一种有毒气体。
8. Rate of Reaction | 反应速率
The rate of a reaction tells us how quickly reactants are used up or products are made. You can measure it by recording the change in mass, volume of gas produced, or colour change over time.
反应速率表明反应物消耗或生成物产生的快慢。你可以通过记录质量的变化、放出气体的体积或颜色随时间的变化来测量反应速率。
Mean rate of reaction = Δ(quantity of product or reactant) / Δtime
In simpler form:
Mean rate = Change in mass or volume / Time taken
For example, if 20 g of zinc reacts completely with acid in 5 minutes, the mean rate = 20 g / 5 min = 4 g/min.
例如，若 20 g 锌与酸在 5 分钟内完全反应，则平均速率 = 20 g / 5 min = 4 g/min。
Factors that increase the rate of reaction: higher temperature, higher concentration of solutions, larger surface area of solids, and the use of a catalyst. These factors increase the frequency of successful collisions between particles.
加快反应速率的因素：升高温度、增大溶液的浓度、增大固体的表面积以及使用催化剂。这些因素都会增加粒子间有效碰撞的频率。
9. pH Scale and Indicators | pH 值与指示剂
The pH scale measures how acidic or alkaline a solution is. It ranges from 0 to 14: pH less than 7 is acidic, pH 7 is neutral, and pH greater than 7 is alkaline.
pH 标度衡量溶液的酸碱度，范围从 0 到 14：pH 小于 7 为酸性，pH 等于 7 为中性，pH 大于 7 为碱性。
Indicators change colour depending on the pH. The table below shows the colour changes of some common indicators.
指示剂会根据 pH 值改变颜色。下表展示了几种常见指示剂的颜色变化。
| Indicator | Colour in acid | Colour in neutral | Colour in alkali |
|---|---|---|---|
| Litmus | Red | Purple | Blue |
| Phenolphthalein | Colourless | Colourless | Pink |
| Methyl orange | Red | Orange | Yellow |
A universal indicator provides a wider range of colours, from red (strong acid) through green (neutral) to purple (strong alkali). It can be used to estimate the pH value more precisely.
通用指示剂能显示更广泛的颜色变化，从红色（强酸）经绿色（中性）到紫色（强碱），可用于更准确地估计 pH 值。
10. Particle Model and State Changes | 粒子模型与状态变化
All matter is made of tiny particles that are constantly moving. The arrangement and movement of these particles determine the state of matter: solid, liquid or gas.
所有物质都由不断运动的微小粒子构成。粒子的排列方式和运动状态决定了物质的状态：固态、液态或气态。
In solids, particles are packed closely in a fixed, regular pattern and vibrate in place. In liquids, particles are close together but can slide past each other. In gases, particles are far apart and move rapidly in all directions.
固体中的粒子紧密排列成固定的规则结构，并在原位振动。液体中的粒子彼此靠近但能相互滑动。气体中的粒子相距很远，向各个方向快速运动。
State changes have specific names and involve energy transfer:
- Melting: solid → liquid (heat absorbed)
- Freezing: liquid → solid (heat released)
- Boiling/evaporating: liquid → gas (heat absorbed)
- Condensing: gas → liquid (heat released)
- Sublimation: solid → gas (heat absorbed) – e.g. solid CO₂ (dry ice)
状态变化有专门名称，并伴随着能量转移：
- 熔化：固态 → 液态（吸热）
- 凝固：液态 → 固态（放热）
- 沸腾/蒸发：液态 → 气态（吸热）
- 冷凝：气态 → 液态（放热）
- 升华：固态 → 气态（吸热）——例如固体 CO₂（干冰）
During melting or boiling, the temperature of the substance stays constant until the whole sample has changed state. This is because the energy is used to overcome the forces between particles, not to raise the temperature.
在熔化或沸腾的过程中，物质的温度保持不变，直到整份样品完全改变状态。这是因为所吸收的能量用于克服粒子间的作用力，而不是用来升高温度。
11. Oxidation and Reduction | 氧化与还原
Oxidation originally meant adding oxygen to a substance. A reaction in which a substance gains oxygen is called an oxidation reaction. For example, when magnesium burns in air, it gains oxygen to form magnesium oxide.
氧化最初指给某物质配上氧气。物质获得氧的反应称为氧化反应。例如，镁在空气中燃烧时获得氧，生成氧化镁。
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