📚 AQA A Level Chemistry June 2018 Paper 5: Unit 5 Revision | AQA A Level 化学 2018年6月试卷5：第五单元复习
This article is a focused revision guide for the AQA A Level Chemistry June 2018 Paper 5. It covers the core topics in Unit 5: energetics, redox equilibria, transition metal chemistry, periodicity and aqueous inorganic reactions.
本文是针对 AQA A Level 化学 2018年6月试卷5的专项复习指南。内容涵盖第五单元的核心主题：能量学、氧化还原平衡、过渡金属化学、周期性以及无机水溶液反应。
Paper 5 is a written paper that tests your ability to apply knowledge to unfamiliar contexts. You need strong calculation skills for energetics, clear explanations for transition metal behaviour, and accurate equations for inorganic reactions.
试卷5是一份笔试，考查你将知识应用于陌生情境的能力。你需要具备扎实的能量学计算能力、清晰的过渡金属行为解释能力以及准确书写无机反应方程式的能力。
Below is a summary of the main topic areas commonly assessed in this paper.
以下是这份试卷中常见考查主题的总结。
| Topic | Typical question style | Key skills |
|---|---|---|
| Energetics and thermodynamics | Born-Haber cycles, entropy, Gibbs free energy calculations | Use of enthalpy cycles, sign conventions, feasibility judgement |
| Redox equilibria | Cell diagrams, Ecell calculations, predicting redox reactions | Standard electrode potentials, cell notation, oxidising/reducing agents |
| Transition metal chemistry | Complexes, isomerism, colour, redox titrations | Ligand substitution, d-d transitions, balanced redox equations |
| Periodicity | Period 3 oxides and chlorides, acid-base character | Reaction equations, pH explanation, structure and bonding |
| Aqueous inorganic chemistry | Reactions of hexaaqua ions, amphoteric hydroxides | Deprotonation, ligand substitution, observations |
1. Born-Haber Cycles and Lattice Enthalpy | Born-Haber 循环与晶格焓
Lattice enthalpy is the enthalpy change when one mole of an ionic lattice is formed from its gaseous ions under standard conditions.
晶格焓是在标准条件下，由气态离子生成一摩尔离子晶格时的焓变。
For sodium chloride, the lattice enthalpy is represented by:
对于氯化钠，晶格焓可表示为：
Na⁺(g) + Cl⁻(g) → NaCl(s) ΔH°latt = −787 kJ mol⁻¹
Lattice enthalpy is always exothermic because energy is released when oppositely charged ions come together to form a solid lattice.
晶格焓始终为放热，因为相反电荷的离子结合形成固体晶格时会释放能量。
A Born-Haber cycle is an energy cycle that links lattice enthalpy to other enthalpy changes such as atomisation, ionisation energy, electron affinity and enthalpy of formation.
Born-Haber 循环是一个能量循环，它将晶格焓与原子化、电离能、电子亲和能以及生成焓等焓变联系起来。
For NaCl, the key steps are:
对于 NaCl，关键步骤如下：
- Na(s) → Na(g) — enthalpy of atomisation of sodium
- ½Cl₂(g) → Cl(g) — enthalpy of atomisation of chlorine
- Na(g) → Na⁺(g) + e⁻ — first ionisation energy of sodium
- Cl(g) + e⁻ → Cl⁻(g) — first electron affinity of chlorine
- Na⁺(g) + Cl⁻(g) → NaCl(s) — lattice enthalpy of NaCl
- Na(s) → Na(g) — 钠的原子化焓
- ½Cl₂(g) → Cl(g) — 氯的原子化焓
- Na(g) → Na⁺(g) + e⁻ — 钠的第一电离能
- Cl(g) + e⁻ → Cl⁻(g) — 氯的第一电子亲和能
- Na⁺(g) + Cl⁻(g) → NaCl(s) — NaCl 的晶格焓
The overall enthalpy change of formation is the sum of all these steps:
总生成焓变是所有这些步骤的总和：
ΔH°f(NaCl) = ΔH°at(Na) + ½ΔH°at(Cl₂) + IE₁(Na) + EA₁(Cl) + ΔH°latt(NaCl)
When using a Born-Haber cycle, always check the direction of the arrows. If a step is reversed, the sign of the enthalpy change must be reversed.
使用 Born-Haber 循环时，务必检查箭头方向。如果某一步被反过来，焓变的符号也必须反转。
Experimental lattice enthalpy values are often more negative than theoretical values calculated from the perfect ionic model. This difference indicates covalent character caused by polarisation of the anion by the cation.
实验晶格焓值通常比用理想离子模型计算的理论值更负。这种差异表明阳离子对阴离子产生极化，从而产生共价性。
2. Enthalpy of Solution and Hydration | 溶解焓与水合焓
Enthalpy of solution is the enthalpy change when one mole of an ionic solid dissolves in a large amount of water to form a very dilute solution.
溶解焓是一摩尔离子固体在大量水中溶解形成极稀溶液时的焓变。
Enthalpy of hydration is the enthalpy change when one mole of gaseous ions dissolves in water to form one mole of aqueous ions.
水合焓是一摩尔气态离子溶于水生成一摩尔水合离子时的焓变。
For a simple ionic compound such as NaCl, the enthalpy of solution can be calculated using the cycle:
对于像 NaCl 这样的简单离子化合物，溶解焓可用以下循环计算：
ΔH°sol = ΔH°hyd(Na⁺) + ΔH°hyd(Cl⁻) − ΔH°latt(NaCl)
Remember that lattice enthalpy of formation is exothermic, but when an ionic solid dissolves, the lattice must be broken. Therefore, the lattice enthalpy term is usually written as the reverse, i.e. lattice dissociation enthalpy, which is endothermic.
请记住，晶格生成焓为放热，但当离子固体溶解时，晶格必须被破坏。因此，晶格焓项通常写作相反方向，即晶格解离焓，为吸热。
Enthalpy of hydration becomes more exothermic as the charge on the ion increases and as the ionic radius decreases, because the ion-dipole attraction with water molecules becomes stronger.
离子的电荷越高、半径越小，水合焓越放热，因为离子与水分子的离子-偶极吸引力更强。
Solubility is not determined only by enthalpy. Entropy changes are also important, especially when ionic compounds dissolve to produce a more disordered solution.
溶解度不仅由焓决定。熵变也很重要，尤其是当离子化合物溶解产生更无序的溶液时。
3. Entropy and Gibbs Free Energy | 熵与吉布斯自由能
Entropy, S, is a measure of the number of ways particles and energy can be arranged. Gases have the highest entropy, followed by liquids and then solids.
熵 S 是粒子和能量排列方式数量的度量。气体的熵最高，液体次之，固体最低。
The standard entropy change for a reaction is calculated using:
反应的标准熵变计算如下：
ΔS° = ΣS°(products) − ΣS°(reactants)
A positive ΔS° means the products are more disordered than the reactants. This often happens when a gas is produced or when a solid dissolves.
ΔS° 为正值表示产物比反应物更无序。当生成气体或固体溶解时，通常会出现这种情况。
The Gibbs free energy change combines enthalpy and entropy to determine whether a reaction is feasible at a given temperature:
吉布斯自由能变结合焓和熵，用于判断反应在一定温度下是否可行：
ΔG = ΔH − TΔS
For a reaction to be feasible, ΔG must be less than or equal to zero. Temperature must be in kelvin, and ΔH and ΔS must have consistent units, usually J mol⁻¹ and J K⁻¹ mol⁻¹.
反应可行需满足 ΔG ≤ 0。温度单位必须为开尔文，ΔH 与 ΔS 的单位必须一致，通常为 J mol⁻¹ 和 J K⁻¹ mol⁻¹。
The table below shows how the signs of ΔH and ΔS affect feasibility.
下表显示了 ΔH 和 ΔS 的符号如何影响反应可行性。
| ΔH | ΔS | Feasibility |
|---|---|---|
| Negative | Positive | Always feasible |
| Positive | Negative | Never feasible |
| Negative | Negative | Feasible at low temperature |
| Positive | Positive | Feasible at high temperature |
ion just becomes feasible, ΔG = 0. The minimum temperature can be found using T = ΔH / ΔS.
在反应刚好可行的温度下，ΔG = 0。最低温度可由 T = ΔH / ΔS 求得。
4. Electrode Potentials and Electrochemical Cells | 电极电势与电化学电池
A standard electrode potential is the potential difference between a half-cell and a standard hydrogen electrode under standard conditions: 298 K, 100 kPa and 1.0 mol dm⁻³ ion concentration.
标准电极电势是半电池与标准氢电极在标准条件（298 K、100 kPa、离子浓度 1.0 mol dm⁻³）下的电势差。
The standard hydrogen electrode consists of hydrogen gas at 100 kPa bubbling over a platinum electrode immersed in 1.0 mol dm⁻³ H⁺ ions.
标准氢电极由 100 kPa 的氢气在浸于 1.0 mol dm⁻³ H⁺ 溶液中的铂电极上鼓泡构成。
A cell diagram is written with the more negative half-cell on the left and the more positive half-cell on the right.
电池图式将较负的半电池写在左边，较正的半电池写在右边。
For example, the zinc-copper cell is written as:
例如，锌-铜电池写作：
Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s)
The standard cell potential is calculated using:
标准电池电势计算如下：
E°cell = E°(right) − E°(left)
A positive E°cell means the reaction is feasible in the forward direction. The species with the more positive E° is the stronger oxidising agent, while the species with the more negative E° is the stronger reducing agent.
E°cell 为正值表示正方向反应可行。E° 更正的物质为较强的氧化剂，而 E° 较负的物质为较强的还原剂。
If a cell reaction is reversed, the sign of E° changes. If the cell equation is multiplied by two, the electrode potential does not double because it is an intensive property.
如果电池反应被反转，E° 的符号改变。如果电池方程乘以系数 2，电极电势不会加倍，因为它是强度性质。
5. Redox Titrations with Transition Metal Ions | 过渡金属离子的氧化还原滴定
Transition metal ions often participate in redox titrations because they can exist in different oxidation states and exhibit clear colour changes.
过渡金属离子常参与氧化还原滴定，因为它们能以不同氧化态存在，并呈现明显的颜色变化。
A common titration is the reaction between acidified potassium manganate(VII) and iron(II) ions:
常见的滴定是酸化高锰酸钾与亚铁离子的反应：
MnO₄⁻(aq) + 5Fe²⁺(aq) + 8H⁺(aq) → Mn²⁺(aq) + 5Fe³⁺(aq) + 4H₂O(l)
The end point is detected by the first permanent pale pink colour caused by excess MnO₄⁻, because MnO₄⁻ is deep purple and Mn²⁺ is almost colourless.
滴定终点通过过量的 MnO₄⁻ 产生的第一个持久的淡粉红色来检测，因为 MnO₄⁻ 为深紫色，而 Mn²⁺ 几乎无色。
Another important redox titration uses potassium dichromate(VI) to oxidise iron(II):
另一种重要的氧化还原滴定使用重铬酸钾(VI)氧化亚铁离子：
Cr₂O₇²⁻(aq) + 6Fe²⁺(aq) + 14H⁺(aq) → 2Cr³⁺(aq) + 6Fe³⁺(aq) + 7H₂O(l)
In the manganate(VII) titration, the ratio MnO₄⁻ : Fe²⁺ is 1 : 5. In the dichromate(VI) titration, the ratio Cr₂O₇²⁻ : Fe²⁺ is 1 : 6.
在高锰酸根滴定中，MnO₄⁻ 与 Fe²⁺ 的化学计量比为 1 : 5。在重铬酸根滴定中，Cr₂O₇²⁻ 与 Fe²⁺ 的化学计量比为 1 : 6。
Always use the balanced equation to find the mole ratio, then work out concentration, mass or percentage purity from the titration data.
务必根据配平方程式确定摩尔比，再利用滴定数据计算浓度、质量或纯度百分比。
6. Transition Metal Complexes and Isomerism | 过渡金属配合物与异构现象
A transition metal complex consists of a central metal ion surrounded by ligands. A ligand is a species that donates a lone pair of electrons to the metal ion to form a coordinate bond.
过渡金属配合物由中心金属离子和周围的配体组成。配体是提供孤对电子给金属离子形成配位键的物种。
Common ligands include water H₂O, ammonia NH₃, chloride Cl⁻ and cyanide CN⁻. Ligands that form one coordinate bond are monodentate; ligands that form more than one are polydentate, such as EDTA⁴⁻.
常见配体包括 H₂O、NH₃、Cl⁻ 和 CN⁻。只形成一个配位键的配体为单齿配体；形成多个配位键的为多齿配体，例如 EDTA⁴⁻。
The coordination number is the number of coordinate bonds formed between the metal ion and its ligands. A coordination number of six usually gives an octahedral shape, while four gives either tetrahedral or square planar.
配位数是金属离子与配体之间形成的配位键数目。配位数为 6 时通常为八面体构型，而配位数为 4 时可为四面体或平面正方形。
Complexes can show cis-trans isomerism when they have two pairs of identical ligands in an octahedral or square planar arrangement.
当配合物在八面体或平面正方形排布中有两对相同配体时，可表现出顺反异构。
For example, [Co(NH₃)₄Cl₂]⁺ exists as a cis isomer, where the two Cl⁻ ligands are adjacent, and a trans isomer, where they are opposite.
例如，[Co(NH₃)₄Cl₂]⁺ 存在顺式异构体（两个 Cl⁻ 配体相邻）和反式异构体（两个 Cl⁻ 配体相对）。
Optical isomerism occurs when a complex has no plane of symmetry and its mirror images are non-superimposable. An example is [Ni(NH₃)₂Cl₂], which can form a tetrahedral chiral complex.
光学异构发生在配合物无对称面且其镜像不可重叠时。例如 [Ni(NH₃)₂Cl₂] 可形成四面体手性配合物。
7. Colour in Transition Metal Complexes | 过渡金属配合物的颜色
Transition metal complexes are often coloured because they absorb visible light. Absorption occurs when electrons are excited between split d-orbitals in the presence of ligands.
过渡金属配合物通常有颜色，因为它们吸收可见光。当配体存在时，d 轨道发生分裂，电子在分裂的 d 轨道之间跃迁而产生吸收。
The colour observed is the complementary colour of the light absorbed. For example, [Cu(H₂O)₆]²⁺ absorbs orange-red light and appears blue.
观察到的颜色是所吸收光的互补色。例如，[Cu(H₂O)₆]²⁺ 吸收橙红色光，呈现蓝色。
The energy difference between the split d-orbitals, Δoct, depends on the ligand. The spectrochemical series places ligands in order of increasing field strength:
分裂 d 轨道之间的能量差 Δoct 取决于配体。光谱化学序列按配体场强递增排列：
Cl⁻ < H₂O < NH₃ < CN⁻
Strong-field ligands such as CN⁻ create a large Δoct and absorb higher-energy light, while weak-field ligands such as Cl⁻ create a small Δoct and absorb lower-energy light.
强场配体如 CN⁻ 产生较大的 Δoct，吸收较高能量的光；而弱场配体如 Cl⁻ 产生较小的 Δoct，吸收较低能量的光。
A change in ligand or oxidation state changes the colour. For example, [Cu(H₂O)₆]²⁺ is blue, but [Cu(NH
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