📚 AS AQA Chemistry Unit 2 Insert Jan19 Revision Guide | AQA AS 化学 Unit 2 2019年1月插页复习指南
This revision guide unpacks the core topics tested in the AS AQA Chemistry Unit 2 January 2019 insert. It covers energetics, kinetics, equilibria, redox and inorganic chemistry, with worked examples and key equations in the same style as the insert data.
本复习指南解析 2019 年 1 月 AQA AS 化学 Unit 2 插页所考查的核心专题。内容包括能量学、动力学、平衡、氧化还原和无机化学，并提供与插页数据风格一致的计算示例和关键方程式。
1. How to Read the Jan19 Insert | 如何阅读 2019 年 1 月插页
The Jan19 insert is a data sheet, not a question paper. It gives atomic numbers, relative atomic masses, bond enthalpies, standard electrode potentials and other constants. Before answering each question, locate the data you need in the insert and write down its exact symbol and unit.
2019 年 1 月插页是数据表，不是试卷。它给出原子序数、相对原子质量、键焓、标准电极电势和其他常数。在回答每一题前，先找到插页中所需的数据，并写出其确切符号和单位。
- Standard enthalpy of combustion ΔHc°, formation ΔHf° and reaction ΔHr° values are given in kJ mol⁻¹.
- 标准燃烧焓 ΔHc°、生成焓 ΔHf° 和反应焓 ΔHr° 的单位均为 kJ mol⁻¹。
- Bond enthalpies are quoted as mean bond enthalpies in kJ mol⁻¹.
- 键焓以平均键焓给出，单位为 kJ mol⁻¹。
- Standard electrode potentials E° are listed for half-cells with the more positive value being the stronger oxidising agent.
- 标准电极电势 E° 按半电池列出，数值越正表示氧化剂越强。
Always transfer the numerical data carefully from the insert to your working. A common error is to copy the sign or unit incorrectly, which loses marks even when the method is correct.
从插页向计算过程抄写数据时务必仔细。常见错误是抄错符号或单位，即使方法正确也会失分。
2. Enthalpy Changes and Calorimetry | 焓变与量热法
he mass of the solution, c is the specific heat capacity and ΔT is the temperature change.
焓变是恒压下转移的热能。在量热法中，溶液吸收或放出的热量用 q = mcΔT 计算，其中 m 是溶液质量，c 是比热容，ΔT 是温度变化。
q = mcΔT
The enthalpy change per mole is then found by dividing q by the number of moles of the limiting reactant.
然后每摩尔焓变等于 q 除以限制反应物的物质的量。
ΔH = -q ÷ n
The negative sign appears when the reaction is exothermic, because heat is released from the system to the surroundings. For endothermic reactions, heat is absorbed, so ΔH is positive.
放热反应要加负号，因为热量从体系释放到环境。吸热反应吸收热量，因此 ΔH 为正。
| Reaction type | Sign of ΔH | Temperature of surroundings |
| Exothermic | Negative | Increases |
| Endothermic | Positive | Decreases |
In a typical Jan19 insert question, you may be asked to calculate ΔH from a temperature rise in a polystyrene cup. Always assume the solution density is 1.00 g cm⁻³ and the specific heat capacity is 4.18 J g⁻¹ K⁻¹ unless stated otherwise.
在 Jan19 插页的常见题中，你可能会根据聚苯乙烯杯中的温升计算 ΔH。除非另有说明，通常假设溶液密度为 1.00 g cm⁻³，比热容为 4.18 J g⁻¹ K⁻¹。
3. Hess's Law and Bond Enthalpies | 盖斯定律与键焓
Hess's law states that the total enthalpy change for a reaction is independent of the route taken. This allows us to use enthalpy of formation or combustion data from the insert to calculate ΔH for a reaction.
盖斯定律指出，反应的总焓变与所经途径无关。因此我们可以利用插页中的生成焓或燃烧焓数据计算反应的 ΔH。
ΔHr° = Σ ΔHf°(products) - Σ ΔHf°(reactants)
Alternatively, mean bond enthalpies can be used because breaking bonds is endothermic and making bonds is exothermic.
另外，可以用平均键焓计算，因为断键吸热而成键放热。
ΔH = Σ bond enthalpies broken - Σ bond enthalpies made
Mean bond enthalpies are average values from many compounds, so answers using them are approximate. The insert data should be used exactly as printed.
平均键焓是来自许多化合物的平均值，因此用其计算的结果是近似值。插页数据应完全按原文使用。
s, then make 2 C=O and 4 O-H bonds. Subtract the energy released from the energy absorbed.
示例：对于 CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)，断裂 4 个 C-H 和 2 个 O=O 键，然后生成 2 个 C=O 和 4 个 O-H 键。用吸收的总能量减去放出的总能量。
4. Reaction Rates and Maxwell-Boltzmann Distribution | 反应速率与麦克斯韦-玻尔兹曼分布
For a reaction to occur, particles must collide with energy greater than or equal to the activation energy Eₐ and in the correct orientation. The Maxwell-Boltzmann distribution shows the range of molecular kinetic energies in a gas at a given temperature.
反应发生要求粒子碰撞的能量必须大于或等于活化能 Eₐ，且取向正确。麦克斯韦-玻尔兹曼分布表示一定温度下气体分子的动能分布范围。
The curve starts at the origin, rises to a peak at the most probable energy, and then tails off to higher energies. The area under the curve represents the total number of particles.
曲线从原点出发，上升到最概然能量处出现峰值，然后向高能方向延伸。曲线下面积代表总粒子数。
Increasing temperature shifts the peak to the right and lowers it, but the area under the curve after Eₐ increases. This means a much larger proportion of particles can react, so the rate increases.
升高温度使峰值右移并降低，但 Eₐ 右侧曲线下面积增大。这意味着能反应的粒子比例大幅增加，因此速率加快。
Adding a catalyst provides an alternative route with a lower activation energy. The Eₐ line shifts to the left, so more particles have enough energy without changing the temperature.
加入催化剂提供了活化能较低的替代路径。Eₐ 线向左移动，因此在温度不变的情况下有更多粒子具有足够能量。
Concentration and pressure affect rate by increasing the number of particles per unit volume, giving more frequent collisions per second.
浓度和压强通过增加单位体积粒子数来影响速率，使每秒碰撞频率增加。
5. Chemical Equilibria and Le Chatelier's Principle | 化学平衡与勒夏特列原理
A reversible reaction reaches dynamic equilibrium when the forward and reverse rates are equal and the concentrations of reactants and products remain constant. Dynamic means both reactions are still occurring.
可逆反应达到动态平衡时，正逆反应速率相等，反应物和产物浓度保持不变。动态意味着两个方向的反应仍在进行。
Le Chatelier's principle states that if a system at equilibrium is subjected to a change, the equilibrium shifts to oppose that change.
勒夏特列原理指出，如果平衡体系受到外界改变，平衡会向削弱这种改变的方向移动。
- Increasing concentration of a reactant shifts equilibrium to the right.
- 增大反应物浓度使平衡向右移动。
- Increasing pressure shifts equilibrium towards the side with fewer gas moles.
- 增大压强使平衡向气体物质的量较少的一侧移动。
- Increasing temperature shifts equilibrium in the endothermic direction.
- 升高温度使平衡向吸热方向移动。
- A catalyst does not shift equilibrium; it only speeds up the rate at which equilibrium is reached.
- 催化剂不会使平衡移动，只会加快达到平衡的速率。
Industrial processes such as the Haber process use a compromise temperature and pressure because a high pressure increases yield but costs more, while a low temperature favours the exothermic forward reaction but reduces rate.
哈伯法等工业过程采用折中的温度和压强，因为高压提高产率但成本更高，而低温有利于放热正反应但会降低速率。
6. Equilibrium Constant Kc | 平衡常数 Kc
For a general homogeneous reaction aA + bB ⇌ cC + dD, the equilibrium constant Kc is:
对于一般均相反应 aA + bB ⇌ cC + dD，平衡常数 Kc 为：
Kc = [C]c [D]d ÷ [A]a [B]b
Square brackets denote concentration in mol dm⁻³. The units of Kc depend on the total number of moles of products minus reactants in the balanced equation.
方括号表示浓度，单位为 mol dm⁻³。Kc 的单位取决于化学方程式中生成物总物质的量减去反应物总物质的量。
Only gases and aqueous species appear in the Kc expression. Solids and pure liquids are omitted because their concentrations are effectively constant.
只有气体和溶液中的物种出现在 Kc 表达式中。固体和纯液体因其浓度基本恒定而省略。
When the reaction quotient equals Kc, the system is at equilibrium. If not, the position shifts until Kc is restored.
当反应商等于 Kc 时，体系处于平衡状态。如果不相等，平衡位置会移动直到重新满足 Kc。
Only temperature changes the value of Kc. Concentration and pressure changes do not affect the value, although they may shift the position of equilibrium.
只有温度会改变 Kc 的数值。浓度和压强变化不会改变 Kc 的值，尽管它们可能使平衡位置移动。
7. Redox and Oxidation States | 氧化还原与氧化数
Oxidation is loss of electrons; reduction is gain of electrons. A redox reaction involves both processes occurring simultaneously. Oxidation states are a bookkeeping tool for tracking electron transfer.
氧化是失去电子，还原是得到电子。氧化还原反应同时包含这两个过程。氧化数是追踪电子转移的工具。
- The oxidation state of an uncombined element is 0.
- 游离态元素的氧化数为 0。
- Hydrogen is +1 except in metal hydrides where it is -1.
- 氢的氧化数为 +1，但在金属氢化物中为 -1。
- Oxygen is -2 except in peroxides and in OF₂.
- 氧的氧化数为 -2，但在过氧化物和 OF₂ 中除外。
- The sum of oxidation states in a neutral compound is 0; in an ion it equals the charge.
- 中性化合物中氧化数总和为 0；离子中氧化数总和等于离子电荷。
In the Jan19 insert, standard electrode potentials allow you to predict whether a redox reaction is feasible. A species with a more positive E° value gains electrons more readily.
在 Jan19 插页中，标准电极电势可用于预测氧化还原反应是否可行。E° 值越正的物种越容易得到电子。
A half-equation shows either oxidation or reduction separately. For example, the reduction of chlorine gas is:
半反应式单独表示氧化或还原过程。例如，氯气的还原为：
Cl₂(g) + 2e⁻ → 2Cl⁻(aq)
The oxidation of zinc is:
锌的氧化为：
Zn(s) → Zn²⁺(aq) + 2e⁻
Combining the two balanced half-equations gives the full ionic redox equation.
将两个配平的半反应式合并，得到完整的离子氧化还原方程式。
8. Group 2: Alkaline Earth Metals | 第 2 族：碱土金属
Group 2 metals react with water to form an alkaline hydroxide and hydrogen gas. Reactivity increases down the group because atomic radius increases and ionisation energy decreases.
第 2 族金属与水反应生成碱性氢氧化物和氢气。反应性沿族向下增强，因为原子半径增大，电离能降低。
Mg(s) + 2H₂O(l) → Mg(OH)₂(aq) + H₂(g)
Reaction with oxygen forms the oxide, while reaction with chlorine forms the chloride. The oxides react with water to give hydroxides with increasing solubility down the group.
与氧反应生成氧化物，与氯反应生成氯化物。氧化物与水反应生成氢氧化物，溶解度沿族向下增大。
Thermal stability of Group 2 carbonates increases down the group. This is because the larger cation polarises the carbonate anion less, making the carbonate harder to decompose.
第 2 族碳酸盐的热稳定性沿族向下增强。这是因为较大的阳离子对碳酸根阴离子的极化作用较弱，使碳酸盐更难分解。
Barium sulfate is insoluble and is used in medical X-ray imaging. Magnesium hydroxide is used as an antacid to neutralise stomach acid.
硫酸钡不溶于水，用于医学 X 射线成像。氢氧化镁用作抗酸剂中和胃酸。
9. Group 7: The Halogens | 第 7 族：卤素
The halogens exist as diatomic molecules. Electronegativity decreases down the group because the bonding pair is further from the nucleus and more shielded.
卤素以双原子分子形式存在。电负性沿族向下降低，因为成键电子对离核更远且屏蔽作用更强。
Boiling points increase down the group because the molecules have more electrons, leading to stronger London dispersion forces between molecules.
沸点沿族向下升高，因为分子中电子更多，分子间的伦敦色散力更强。
A more reactive halogen displaces a less reactive halide from solution. Reactivity decreases down the group. For example, chlorine displaces bromide ions.
较活泼的卤素能将较不活泼的卤离子从溶液中置换出来。反应性沿族向下减弱。例如，氯置换溴离子。
Cl₂(aq) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq)
In aqueous displacement reactions, a colour change is observed. Bromine water is orange, iodine solution is brown, and chlorine water is pale green.
在水溶液置换反应中可观察到颜色变化。溴水为橙色，碘溶液为棕色，氯水为浅绿色。
10. Halide Tests and Redox in Aqueous Solution | 卤离子检验与溶液中的氧化还原
Adding silver nitrate solution to a solution containing halide ions gives a precipitate of silver halide. Different halides give different coloured precipitates.
向含卤离子的溶液中加入硝酸银溶液，会生成卤化银沉淀。不同卤离子产生不同颜色的沉淀。
| Halide ion | Precipitate colour | Solubility in NH₃(aq) |
| Cl⁻ | White | Soluble in dilute NH₃ |
| Br⁻ | Cream | Soluble in concentrated NH₃ |
| I⁻ | Yellow | Insoluble in concentrated NH₃ |
Chlorine gas oxidises bromide ions to bromine and iodide ions to iodine. Bromine oxidises iodide ions but not chloride ions. This order matches the decreasing oxidising power of the halogens down the group.
氯气将溴离子氧化为溴，将碘离子氧化为碘。溴能氧化碘离子但不能氧化氯离子。这一顺序符合卤素沿族向下氧化能力减弱的规律。
Concentrated sulfuric acid is a stronger oxidising agent and reacts further with bromide and iodide ions, producing HBr and HI which are then oxidised to Br₂ and I₂ along with sulfur dioxide and hydrogen sulfide.
浓硫酸是更强的氧化剂，会进一步与溴离子和碘离子反应，生成的 HBr 和 HI 随后被氧化为 Br₂ 和 I₂，同时产生二氧化硫和硫化氢。
11. Required Practical and Graph Skills | 必需的实验与图表技能
Unit 2 practical skills include measuring enthalpy changes, following reaction progress, and testing for ions. In the Jan19 insert, you may be given raw results and asked to complete calculations or plot graphs.
Unit 2 的实验技能包括测量焓变、跟踪反应进程和检验离子。在 Jan19 插页中，可能会给出原始实验结果并要求你完成计算或绘制图形。
When plotting a graph, label both axes with quantity and unit, choose a sensible scale, plot points with small crosses, and draw a best-fit line. For enthalpy practicals, plot temperature against time and extrapolate back to the mixing time to correct for heat loss.
绘图时，两个坐标轴都要标注物理量和单位，选择合理分度，用十字标出数据点，并画出最佳拟合线。对于焓实验，绘制温度随时间的变化图，并外推回混合时间以校正热损失。
Calculating percentage error and identifying systematic errors such as heat loss, incomplete combustion or slow reaction are common examiner targets. Always suggest improvements such as insulation, stirring or repeating.
计算百分误差并识别系统误差（如热量散失、燃烧不完全或反应缓慢）是常见考点。改进措施通常包括保温、搅拌或重复实验。
12. Exam Tips for Unit 2 Insert Questions | Unit 2 插页题应试技巧
Before writing, underline the command words such as describe, explain, calculate or suggest. Each requires a different answer style. Describe asks for facts and observations; explain asks for reasons using chemical principles.
答题前先圈出指令词，如 describe、explain、calculate 或 suggest。它们要求的答题方式不同。Describe 要求陈述事实和现象；explain 要求用化学原理解释原因。
Always include state symbols in equations, balance charges in ionic equations, and show all steps in calculations. Even if the final answer is wrong, method marks can be earned.
方程式要写状态符号，离子方程式要配平电荷，计算题要写出所有步骤。即使最终答案错误，也能获得方法分。
Use the insert data accurately. If a value is given for a bond enthalpy, use that exact value rather than relying on memory. Check significant figures and units at the end.
准确使用插页数据。如果给出键焓等数值，应使用该精确值，而不是凭记忆。最后检查有效数字和单位。
For equilibrium questions, avoid saying a catalyst increases yield. It only increases rate. For redox questions, remember that oxidation state changes must balance with electron transfer.
对于平衡题，不要写催化剂提高产率。催化剂只加快速率。对于氧化还原题，记住氧化数变化必须与电子转移平衡。
When describing observations, state both the starting and final colour. For example: 'a colourless solution turns brown' is better than 'the solution changed colour'.
描述现象时，要同时说明初始颜色和最终颜色。例如“无色溶液变为棕色”比“溶液变色”更好。
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