A-Level Edexcel Chemistry: Formula Summary Handbook | A-Level Edexcel 化学：公式汇总手册

📚 A-Level Edexcel Chemistry: Formula Summary Handbook | A-Level Edexcel 化学：公式汇总手册

This comprehensive handbook brings together all the essential equations and formula relationships required for A-Level Edexcel Chemistry. From the mole concept and gas laws to energetics, kinetics, equilibrium, acid-base chemistry, and redox, every key expression is presented alongside clear explanations. Use this reference to consolidate your understanding, check your calculations, and build confidence for every exam paper.

这本全面的公式手册汇集了 A-Level Edexcel 化学所需的所有基本方程式与公式关系。从摩尔概念、气体定律，到能量学、动力学、平衡、酸碱化学和氧化还原，每个关键表达式都配有清晰的解释。用这份参考资料来巩固理解、核对计算，并在每张试卷中树立信心。

1. The Mole and Molar Calculations | 摩尔与摩尔计算

The mole is the bridge between the microscopic world of atoms and the macroscopic world of measurable masses. The fundamental equation linking mass, molar mass, and amount of substance is a cornerstone of quantitative chemistry.

摩尔是连接微观原子世界与宏观可测量质量的桥梁。将质量、摩尔质量和物质的量联系在一起的基本方程是定量化学的基石。

n = m ÷ M	n = amount of substance (mol), m = mass (g), M = molar mass (g mol⁻¹)
n = V (gas at RTP) ÷ 24.0	n = amount (mol), V = volume of gas at room temperature and pressure (dm³); 24.0 dm³ mol⁻¹ at 298 K and 101 kPa
n = c × V	n = amount (mol), c = concentration (mol dm⁻³), V = volume of solution (dm³)
Number of particles = n × Nₐ	Nₐ = Avogadro constant (6.02 × 10²³ mol⁻¹)

In stoichiometric calculations, these equations allow you to convert between mass, gas volume, solution volume and number of particles, provided the reaction equation is balanced.

在化学计量计算中，这些方程使你能在质量、气体体积、溶液体积和粒子数之间进行转换，前提是反应方程式已配平。

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2. Empirical and Molecular Formulae | 实验式与分子式

An empirical formula gives the simplest whole-number ratio of atoms in a compound, while the molecular formula shows the actual number of each type of atom. The two are related by a multiplier found from the molar mass.

实验式给出化合物中原子的最简整数比，而分子式显示每种原子的实际数目。两者通过由摩尔质量求得的倍数相关联。

Empirical formula	Determined from % composition or mass data: convert masses to moles, divide by smallest mole number to get simplest ratio.
Molecular formula = (Empirical formula)ₙ	n = relative molecular mass ÷ empirical formula mass

For example, if the empirical formula mass of CH₂ is 14.0 and the relative molecular mass is 56.0, then n = 56.0 / 14.0 = 4, giving the molecular formula C₄H₈.

例如，若 CH₂ 的实验式质量为 14.0，相对分子质量为 56.0，则 n = 56.0 / 14.0 = 4，得到分子式 C₄H₈。

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3. The Ideal Gas Equation | 理想气体状态方程

For a gas that behaves ideally, the relationship among pressure, volume, temperature, and amount is given by the ideal gas equation. While Edexcel questions often use the molar volume at RTP, you must also be able to use this equation.

对于表现理想的气体，压力、体积、温度和物质的量之间的关系由理想气体状态方程给出。虽然爱德思考题常使用常温常压下的摩尔体积，但你也必须会用该方程。

pV = nRT

p = pressure (Pa)	V = volume (m³)
n = amount (mol)	R = gas constant = 8.31 J K⁻¹ mol⁻¹
T = temperature (K)	Remember to convert °C to K by adding 273.

This equation can be used to find the Mr of a volatile liquid or to calculate the volume of gas produced in a reaction under non-standard conditions.

此方程可用于求算易挥发液体的相对分子质量，或计算非标准状况下反应产生的气体体积。

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4. Enthalpy Changes and Calorimetry | 焓变与量热法

The heat energy transferred in a chemical reaction can be measured experimentally using the equation q = mcΔT. From this, the molar enthalpy change is calculated.

化学反应中传递的热能可通过实验用公式 q = mcΔT 测得。由此可计算摩尔焓变。

q = m c ΔT

q = heat energy (J); m = mass of solution (g), usually approximate to volume of water in cm³; c = specific heat capacity (4.18 J g⁻¹ K⁻¹ for water); ΔT = temperature change (K or °C).

To obtain the enthalpy change per mole, divide q by the number of moles of the limiting reactant: ΔH = –q ÷ n (with sign convention: – for exothermic, + for endothermic). Pay attention to units: ΔH is typically reported in kJ mol⁻¹, so convert q from J to kJ by dividing by 1000.

为得到每摩尔的焓变，用 q 除以限制反应物的物质的量：ΔH = –q ÷ n（符号惯例：放热为 –，吸热为 +）。注意单位：ΔH 通常以 kJ mol⁻¹ 表示，因此需将 q 从 J 转换为 kJ 除以 1000。

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5. Hess’s Law and Bond Enthalpies | 赫斯定律与键焓

Hess’s Law states that the total enthalpy change for a reaction is independent of the route taken. It is applied using enthalpy changes of formation or combustion.

赫斯定律指出，反应的总焓变与所采取的途径无关。它可利用生成焓变或燃烧焓变进行应用。

ΔH°ᵣₑₐ꜀ₜᵢₒₙ = Σ ΔH°f(products) – Σ ΔH°f(reactants)

ΔH°ᵣₑₐ꜀ₜᵢₒₙ = Σ ΔH°c(reactants) – Σ ΔH°c(products)

Bond enthalpies offer another route: the energy required to break bonds in reactants is compared with the energy released when new bonds form in products.

键焓提供另一途径：比较断裂反应物中的键所需能量与生成物中新键形成时释放的能量。

ΔH ≈ Σ (bond enthalpies broken) – Σ (bond enthalpies made)

Mean bond enthalpy values give only approximate ΔH values because they are averaged over many compounds.

平均键焓值只能给出近似的 ΔH 值，因为它们是在许多化合物中平均得到的。

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6. Rate Equations | 速率方程

The rate equation links the rate of a reaction to the concentrations of certain reactants, each raised to a power called the order with respect to that reactant.

速率方程将反应速率与特定反应物的浓度联系起来，每个浓度项带有幂指数，称为对该反应物的级数。

rate = k [A]ᵐ [B]ⁿ

rate	Usually measured in mol dm⁻³ s⁻¹
k	Rate constant; units depend on overall order
[A], [B]	Concentrations (mol dm⁻³)
m, n	Orders; typically 0, 1 or 2 for A-Level

The overall order is m + n. Rate–concentration data can be analysed graphically or by the initial rates method to deduce orders and hence the rate equation.

总级数为 m + n。速率 – 浓度数据可通过图形法或初始速率法分析，从而推断出级数并得到速率方程。

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7. Equilibrium Constant Kc | 平衡常数 Kc

For a homogeneous system in dynamic equilibrium, the equilibrium constant Kc expresses the ratio of product concentrations to reactant concentrations, each raised to the power of its stoichiometric coefficient.

对于处于动态平衡的均相体系，平衡常数 Kc 表示生成物浓度与反应物浓度的比值，每种浓度以其化学计量系数为指数。

aA + bB ⇌ cC + dD

Kc = [C]ᶜ [D]ᵈ / [A]ᵃ [B]ᵇ

Only species in the same phase (usually aqueous or gaseous) appear in the Kc expression; solids and pure liquids are omitted. Temperature is the only factor that changes the value of Kc. If Kc >> 1, the equilibrium lies to the right; if Kc << 1, it lies to the left.

只有同相物质（通常为水溶液或气体）出现在 Kc 表达式中；固体和纯液体被省略。温度是唯一改变 Kc 值的因素。若 Kc >> 1，平衡向右移动；若 Kc << 1，平衡向左移动。

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8. Equilibrium Constant Kp | 平衡常数 Kp

For gaseous equilibria, the equilibrium constant can be expressed in terms of partial pressures. The partial pressure of a gas is its mole fraction multiplied by the total pressure.

对于气体平衡，平衡常数可用分压表示。一种气体的分压等于其摩尔分数乘以总压。

partial pressure (pₐ) = mole fraction (xₐ) × total pressure (P)

mole fraction of A = moles of A ÷ total moles in gas mixture

For the general reaction aA(g) + bB(g) ⇌ cC(g) + dD(g):

Kp = (pC)ᶜ (pD)ᵈ / (pA)ᵃ (pB)ᵇ

Kp has units, usually derived from the powers of pressure (often atm or Pa). Like Kc, Kp is constant for a given temperature. A change in total pressure does not alter Kp but may shift the equilibrium position.

Kp 有单位，通常由压力的幂次确定（常用 atm 或 Pa）。与 Kc 一样，Kp 在给定温度下为常数。总压的改变不会改变 Kp，但可能使平衡位置发生移动。

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9. Acids and Bases: pH, Ka and pKa | 酸与碱：pH、Ka 和 pKa

The pH scale measures the acidity of an aqueous solution. For strong acids, complete dissociation allows direct calculation from concentration; for weak acids, an equilibrium expression is used.

pH 标度衡量水溶液的酸度。对于强酸，完全解离允许直接从浓度计算；对于弱酸，使用平衡表达式。

pH = –log₁₀ [H⁺]	[H⁺] in mol dm⁻³
[H⁺] = 10⁻ᵖᴴ
Ka = [H⁺][A⁻] / [HA]	Weak acid dissociation constant
pKa = –log₁₀ Ka

For a weak acid, if the degree of dissociation is very small, [HA] ≈ initial concentration, and [H⁺] can be approximated by √(Ka × [HA]). For buffer solutions, the Henderson–Hasselbalch equation is useful: pH = pKa + log([salt]/[acid]).

对于弱酸，若解离度非常小，[HA] ≈ 初始浓度，[H⁺] 可近似为 √(Ka × [HA])。对于缓冲溶液，Henderson–Hasselbalch 方程十分有用：pH = pKa + log([盐]/[酸])。

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10. Ionic Product of Water, Kw | 水的离子积 Kw

Water self-ionises slightly, forming H⁺ and OH⁻ ions. The ionic product of water, Kw, links these concentrations and varies with temperature.

水微弱地自偶电离，生成 H⁺ 和 OH⁻ 离子。水的离子积 Kw 将这些浓度联系起来，并随温度变化。

H₂O(l) ⇌ H⁺(aq) + OH⁻(aq)

Kw = [H⁺][OH⁻]

At 298 K, Kw = 1.0 × 10⁻¹⁴ mol² dm⁻⁶. This means in pure water, [H⁺] = [OH⁻] = 1.0 × 10⁻⁷ mol dm⁻³, giving a neutral pH of 7.00 at this temperature. As temperature increases, Kw increases because ionisation is endothermic. The relationship pKw = pH + pOH is also often used.

在 298 K 时，Kw = 1.0 × 10⁻¹⁴ mol² dm⁻⁶。这意味着纯水中 [H⁺] = [OH⁻] = 1.0 × 10⁻⁷ mol dm⁻³，该温度下中性 pH 为 7.00。随着温度升高，Kw 增大，因为电离是吸热的。pH + pOH = pKw 的关系也经常使用。

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11. Electrode Potentials and the Nernst Equation | 电极电势与能斯特方程

The feasibility of a redox reaction is judged by the standard cell potential (E°cell). The Nernst equation allows you to calculate the potential under non-standard conditions.

氧化还原反应的可行性由标准电池电动势 (E°cell) 判断。能斯特方程使你能够计算非标准条件下的电势。

E°cell = E° (right electrode) – E° (left electrode)

For a reaction, if E°cell > 0, the forward reaction is thermodynamically feasible.

对于一个反应，如果 E°cell > 0，正向反应在热力学上是可行的。

Nernst equation: E = E° + (RT / nF) ln (oxidised / reduced)

At 298 K, this simplifies to: E = E° + (0.059 / n) log₁₀ ([oxidised] / [reduced]) for a reduction half-cell. Here, n is the number of electrons transferred in the half-reaction, F = 96,500 C mol⁻¹.

在 298 K 时，该式简化为：E = E° + (0.059 / n) log₁₀ ([氧化态] / [还原态])，适用于还原半电池。其中 n 是半反应中转移的电子数，F = 96,500 C mol⁻¹。

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12. Key Quantitative Organic Relationships | 关键定量有机关系

In organic chemistry, several trends and calculations are regularly examined, including combustion analysis, degree of unsaturation, and yields.

在有机化学中，若干规律和计算经常被考查，包括燃烧分析、不饱和度和产率。

Degree of unsaturation (IHD) = (2C + 2 – H – X + N) / 2	Where C = number of carbons, H = hydrogens, X = halogens (counted as hydrogens), N = nitrogens. Each double bond or ring contributes 1 IHD unit; triple bonds contribute 2.
Percentage yield = (actual yield ÷ theoretical yield) × 100	Used to assess the efficiency of a synthesis.
Atom economy = (Mr of desired product ÷ Σ Mr of all reactants) × 100	Important in green chemistry.

Combustion analysis data can be used to find the empirical formula of organic compounds by converting masses of CO₂ and H₂O into masses of C and H.

燃烧分析数据可用于求出有机化合物的实验式，通过将 CO₂ 和 H₂O 的质量转化为 C 和 H 的质量。

Published by TutorHao | Chemistry Revision Series | aleveler.com

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