📚 Mastering AQA International A-level Chemistry CH05: Thermodynamics, Equilibria and Organic Analysis | 精通 AQA 国际 A-level 化学 CH05：热力学、平衡与有机分析
This revision guide covers the core knowledge and skills assessed in AQA International A-level Chemistry Unit 5 (CH05). It links thermodynamics, equilibrium, redox, transition metal chemistry and organic structure determination so you can approach the June 2023 paper with confidence. Use the paired English-Chinese explanations to reinforce both understanding and command of key terms.
本复习指南涵盖 AQA 国际 A-level 化学第五单元（CH05）评估的核心知识与技能。它将热力学、平衡、氧化还原、过渡金属化学和有机结构测定联系起来，帮助你自信应对 2023 年 6 月试卷。中英对照解释有助于巩固理解并掌握关键术语。
1. Thermodynamics: Born-Haber Cycles | 热力学：玻恩-哈伯循环
Born-Haber cycles are used to calculate lattice enthalpy by applying Hess's law to the formation of an ionic compound from its elements. The cycle combines atomisation enthalpy, successive ionisation energies, electron affinities and lattice enthalpy. Lattice enthalpy becomes more negative when ions have higher charge and smaller ionic radius, indicating stronger ionic bonding.
玻恩-哈伯循环通过盖斯定律将离子化合物由元素生成的反应路径分解，从而计算晶格焓。该循环综合了原子化焓、逐级电离能、电子亲和能和晶格焓。离子电荷越高、半径越小，晶格焓越负，表明离子键越强。
ΔH°f = ΔH°at + ΣIE + ΣEA + ΔH°lattice
Always label each step clearly and pay attention to sign conventions. Atomisation and ionisation energies are endothermic, while most electron affinities and lattice formation are exothermic. A complete cycle must start and finish at the same energy level.
务必清晰标注每一步，并注意符号约定。原子化和电离能是吸热的，而大多数电子亲和能和晶格形成是放热的。完整的循环必须起点和终点处于同一能级。
2. Entropy and Gibbs Free Energy | 熵与吉布斯自由能
Entropy, S, measures the dispersal of energy in a system. It increases when a substance changes from solid to liquid to gas, when a solid dissolves, or when the number of gas molecules increases in a reaction. A reaction is thermodynamically feasible only when the total entropy change of the system and surroundings is positive.
熵 S 衡量系统中能量的分散程度。物质由固态变为液态再变为气态、固体溶解或反应中气体分子数增加时，熵增大。只有当体系与周围的总熵变为正时，反应在热力学上才可行。
ΔG = ΔH – TΔS
kJ mol⁻¹. At the temperature where ΔG = 0, the reaction becomes feasible, and T = ΔH / ΔS.
反应可行要求 ΔG 为负。将 ΔS 与以 kJ mol⁻¹ 为单位的 ΔH 结合前，记得先把 ΔS 从 J K⁻¹ mol⁻¹ 转换为 kJ K⁻¹ mol⁻¹。当 ΔG = 0 时反应开始可行，此时 T = ΔH / ΔS。
3. Chemical Equilibrium and Kp | 化学平衡与 Kp
For gaseous equilibria, the equilibrium constant Kp is expressed in terms of partial pressures. Each partial pressure is calculated as mole fraction multiplied by total pressure. Kp has no units only when the total number of gas moles is the same on both sides of the equation; otherwise units depend on the stoichiometry.
对于气体平衡，平衡常数 Kp 用分压表示。每个分压等于摩尔分数乘以总压。只有当方程式两边气体总摩尔数相同时 Kp 才无单位；否则单位取决于化学计量数。
Kp = (pC × pD) / (pA × pB) for A + B ⇌ C + D
Pressure changes do not alter Kp at constant temperature, but they can shift the position of equilibrium. A catalyst speeds up both forward and reverse reactions equally and therefore has no effect on Kp or equilibrium position.
恒温下压力变化不会改变 Kp，但会移动平衡位置。催化剂同等程度加快正逆反应，因此对 Kp 或平衡位置均无影响。
4. Acid-Base Equilibria and Buffers | 酸碱平衡与缓冲溶液
A weak acid only partially dissociates in water, so its acid dissociation constant Ka is small. For a weak acid HA, the hydrogen ion concentration can be approximated by the square root of Ka multiplied by the initial acid concentration. pH is then –log₁₀[H⁺].
弱酸在水中仅部分解离，因此其酸解离常数 Ka 很小。对于弱酸 HA，氢离子浓度近似等于 Ka 乘以初始酸浓度的平方根。pH 随之等于 –log₁₀[H⁺]。
pH = pKa + log([A⁻] / [HA])
A buffer solution contains a weak acid and its conjugate base, or a weak base and its conjugate acid. It resists changes in pH when small amounts of acid or base are added because the equilibrium shifts to consume the added H⁺ or OH⁻. The Henderson-Hasselbalch equation above is used to calculate buffer pH.
缓冲溶液含有弱酸及其共轭碱，或弱碱及其共轭酸。加入少量酸或碱时，由于平衡移动消耗加入的 H⁺ 或 OH⁻，溶液的 pH 得以保持稳定。上述亨德森-哈塞尔巴尔赫方程用于计算缓冲溶液的 pH。
5. Electrode Potentials and Electrochemical Cells | 电极电势与电化学电池
Standard electrode potential E° is the emf of a half-cell connected to a standard hydrogen electrode under standard conditions: 298 K, 100 kPa pressure and 1.0 mol dm⁻³ ion concentrations. The more positive E° value means the species is more readily reduced and acts as the oxidising agent.
标准电极电势 E° 是半电池与标准氢电极在标准条件下连接时的电动势：298 K、100 kPa 压力以及 1.0 mol dm⁻³ 离子浓度。E° 值越正，表示该物种越容易被还原，充当氧化剂。
E°cell = E°(reduction) – E°(oxidation)
Electrons flow in the external circuit from the half-cell with the more negative E° to the half-cell with the more positive E°. A redox reaction is feasible if the calculated cell emf is positive. However, kinetic factors such as high activation energy may prevent a thermodynamically feasible reaction from occurring.
电子在外电路中从 E° 较负的半电池流向 E° 较正的半电池。若计算出的电池电动势为正，则该氧化还原反应可行。但高活化能等动力学因素可能阻止热力学上可行的反应实际发生。
6. Transition Metals and Complex Ions | 过渡金属与配位离子
Transition metals form complex ions in which a central metal ion is surrounded by ligands that donate lone pairs of electrons. Common ligands include water, ammonia and chloride ions. The shape of a complex depends mainly on coordination number: six-coordinate complexes are usually octahedral, while four-coordinate complexes may be tetrahedral or square planar.
过渡金属形成配位离子，中心金属离子被提供孤对电子的配体包围。常见配体包括水、氨和氯离子。配离子的形状主要取决于配位数：六配位通常为八面体，四配位可为四面体或平面正方形。
- H₂O: octahedral, coordination number 6
- NH₃: octahedral, coordination number 6
- Cl⁻: tetrahedral, coordination number 4
- H₂O：八面体，配位数为 6
- NH₃：八面体，配位数为 6
- Cl⁻：四面体，配位数为 4
Colour in transition metal complexes arises from d-d electron transitions. When ligands approach the metal ion, the five d orbitals split into two energy levels. Visible light absorption promotes an electron from the lower to the upper level, and the transmitted light appears coloured.
过渡金属配合物的颜色来自 d-d 电子跃迁。配体靠近金属离子时，五个 d 轨道分裂为两个能级。吸收可见光使电子从低能级跃迁到高能级，透射光呈现颜色。
7. Aromatic Chemistry: Electrophilic Substitution | 芳香化学：亲电取代
Benzene has a delocalised ring of six π electrons above and below the plane of carbon atoms. This stability explains why benzene undergoes electrophilic substitution rather than addition. Addition would destroy the delocalised system and lose resonance energy.
苯在碳原子平面上下具有由六个 π 电子组成的离域环。这种稳定性解释了苯发生亲电取代而非加成的原因。加成会破坏离域体系并损失共振能。
C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O
Nitration uses concentrated nitric acid with concentrated sulfuric acid as catalyst. The electrophile is the nitronium ion NO₂⁺, formed by protonation and dehydration of nitric acid. Friedel-Crafts reactions use AlCl₃ as a catalyst to generate alkyl or acyl electrophiles.
硝化反应使用浓硝酸，并以浓硫酸为催化剂。亲电试剂是由硝酸质子化和脱水生成的硝酰阳离子 NO₂⁺。傅克反应使用 AlCl₃ 作为催化剂生成烷基或酰基亲电试剂。
8. Carbonyl and Carboxylic Acid Derivatives | 羰基与羧酸衍生物
Aldehydes and ketones both react with 2,4-dinitrophenylhydrazine to form orange crystals, so this test confirms a carbonyl group. Tollens' reagent contains silver nitrate in aqueous ammonia and oxidises aldehydes to carboxylic acids, producing a silver mirror. Ketones give no Tollens reaction.
醛和酮都与 2,4-二硝基苯肼反应生成橙色晶体，因此该试验可确认羰基的存在。托伦试剂含有氨水中的硝酸银，可将醛氧化为羧酸并生成银镜。酮不发生托伦反应。
Carboxylic acids react with alcohols in the presence of an acid catalyst to form esters and water. Acyl chlorides are far more reactive and react rapidly with alcohols, phenols, ammonia and amines to give esters or amides. This reactivity difference is explained by the stronger electron-withdrawing effect of chlorine compared with hydroxyl.
羧酸在酸催化下与醇反应生成酯和水。酰氯反应活性高得多，能迅速与醇、酚、氨和胺反应生成酯或酰胺。这种反应活性差异可解释为氯的吸电子效应比羟基更强。
9. Amines, Amino Acids and Polymers | 胺、氨基酸与聚合物
Primary amines contain the –NH₂ functional group and act as Brønsted-Lowry bases because the nitrogen lone pair accepts protons. They are also nucleophiles and react with halogenoalkanes to form secondary and tertiary amines. Amino acids contain both –NH₂ and –COOH groups and exist as zwitterions at their isoelectric point.
伯胺含有 –NH₂ 官能团，由于氮孤对电子接受质子，可作布朗斯特-劳里碱。它们也是亲核试剂，可与卤代烷反应生成仲胺和叔胺。氨基酸同时含有 –NH₂ 和 –COOH 基团，在等电点以两性离子形式存在。
Addition polymers form from alkenes or substituted alkenes by a free-radical or ionic chain reaction, with no small molecule lost. Condensation polymers such as polyesters and polyamides form when bifunctional monomers react and eliminate small molecules like water or HCl.
加聚物由烯烃或取代烯烃通过自由基或离子链反应形成，不失去小分子。缩聚物如聚酯和聚酰胺由双官能团单体反应并消去水或 HCl 等小分子形成。
10. Structure Determination: NMR and IR | 结构测定：核磁共振与红外光谱
tional groups from characteristic bond absorptions. A carbonyl C=O stretch appears at 1680–1750 cm⁻¹, and an alcohol O–H bond gives a broad absorption around 3200–3550 cm⁻¹. A nitrile C≡N absorbs around 2220–2260 cm⁻¹.
红外光谱通过特征键吸收识别官能团。羰基 C=O 伸缩振动出现在 1680–1750 cm⁻¹，醇 O–H 键在约 3200–3550 cm⁻¹ 产生宽吸收。腈 C≡N 在 2220–2260 cm⁻¹ 附近吸收。
| Bond | Waven
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