📚 Year 12 OCR Chemistry: Formula & Theorem Quick-Reference Handbook | Year 12 OCR 化学：公式定理速查手册
This article provides a fast and reliable summary of every essential formula, constant and theorem needed for OCR A Level Chemistry Year 12. Use it as a checklist for problem solving, required practicals and exam revision.
本文快速汇总了 OCR A Level 化学第一学年所需的每一个关键公式、常数和定理，可作为解题、必修实验及考试复习的速查清单。
1. The Mole & Mass Relationship | 摩尔与质量关系
The amount of substance, n (mol), is calculated by dividing mass m (g) by molar mass M (g mol⁻¹).
物质的量 n (mol) 由质量 m (g) 除以摩尔质量 M (g mol⁻¹) 计算。
n = m / M
The number of particles N is found by multiplying n by the Avogadro constant Nₐ (6.022 × 10²³ mol⁻¹).
微粒数 N 通过 n 乘以阿伏伽德罗常数 Nₐ (6.022 × 10²³ mol⁻¹) 求得。
N = n × Nₐ
2. Empirical & Molecular Formulae | 实验式与分子式
To find the empirical formula, convert percentage or mass of each element to moles using n = m / Aᵣ, then divide by the smallest number of moles to obtain the simplest whole-number ratio.
求实验式时，先将各元素的质量或百分比用 n = m / Aᵣ 换算成物质的量，然后除以最小物质的量得到最简整数比。
The molecular formula is a whole-number multiple of the empirical formula: molecular formula = (empirical formula)ₙ, where n = relative molecular mass / empirical formula mass.
分子式是实验式的整数倍：分子式 = (实验式)ₙ，其中 n = 相对分子质量 / 实验式质量。
3. Molar Volume & Ideal Gas Equation | 摩尔体积与理想气体状态方程
The ideal gas equation relates pressure, volume, temperature and amount: pV = nRT, where p is in Pa, V in m³, T in K, and R = 8.31 J mol⁻¹ K⁻¹.
理想气体状态方程将压强、体积、温度和物质的量联系起来：pV = nRT，式中 p 单位为 Pa，V 为 m³，T 为 K，R = 8.31 J mol⁻¹ K⁻¹。
pV = nRT
At room temperature and pressure (RTP, 20 °C, 1 atm), the molar volume of any gas is 24.0 dm³ mol⁻¹. Volume (dm³) = n × 24.0.
在常温常压下（RTP, 20 °C, 1 atm），任何气体的摩尔体积为 24.0 dm³ mol⁻¹。体积 (dm³) = n × 24.0。
V (dm³) = n × 24.0
4. Concentration, Titration & Dilution | 浓度、滴定与稀释
Concentration c (mol dm⁻³) is defined as amount of solute n (mol) dissolved in volume V (dm³) of solution.
浓度 c (mol dm⁻³) 定义为溶质物质的量 n (mol) 除以溶液体积 V (dm³)。
c = n / V
In titrations, the equation n = c × V is used repeatedly; remember to convert cm³ to dm³ by dividing by 1000.
滴定中反复使用 n = c × V，注意将 cm³ 转换为 dm³（除以 1000）。
Dilution of a stock solution preserves the number of moles of solute.
稀释储备溶液时溶质物质的量保持不变。
c₁V₁ = c₂V₂
5. Atom Economy & Percentage Yield | 原子经济性与百分产率
Percentage yield compares actual mass obtained to the theoretical mass calculated from the limiting reagent.
百分产率将实际获得的质量与由限量试剂算出的理论质量进行比较。
% yield = (actual yield / theoretical yield) × 100%
Atom economy measures the proportion of reactant atoms that end up in the desired product.
原子经济性衡量反应物原子进入目标产物的比例。
% atom economy = (molar mass of desired product / total molar mass of all products) × 100%
6. Calorimetry & Enthalpy Calculation | 量热法与焓变计算
Heat energy transferred during a reaction in solution is calculated using q = mcΔT, where m is mass of water/solution (g), c = 4.18 J g⁻¹ °C⁻¹ (specific heat capacity of water), and ΔT is the temperature change.
溶液中反应传递的热量用 q = mcΔT 计算，m 为水或溶液质量 (g)，c = 4.18 J g⁻¹ °C⁻¹（水的比热容），ΔT 为温度变化。
q = mcΔT
Enthalpy change ΔH is found by dividing the energy released by the amount of limiting reactant, with a negative sign for exothermic processes (temperature rise).
焓变 ΔH 由释放的能量除以限制反应物的物质的量得出，放热时取负号（温度升高）。
ΔH = –q / n
7. Hess’s Law | 盖斯定律
Hess’s Law states that the total enthalpy change for a reaction is independent of the route taken, depending only on the initial and final states.
盖斯定律指出，反应的总焓变与途径无关，只取决于始态和终态。
To find an unknown ΔH, construct an enthalpy cycle: ΔH(reaction) = ΣΔH (known steps), commonly using enthalpies of combustion or formation.
为求未知 ΔH，可构建焓循环：ΔH(反应) = ΣΔH(已知步骤)，常利用燃烧焓或生成焓数据。
8. Bond Enthalpy Calculations | 键能计算
Mean bond enthalpy is the energy required to break one mole of a given bond, averaged over a range of compounds.
平均键能是断裂 1 摩尔特定键所需的能量，是在不同化合物中取平均值。
Reaction enthalpy change approximates ΔH ≈ Σ E(bonds broken) – Σ E(bonds formed). This is for gases; for liquids/solids, state changes must also be considered.
反应焓变可近似为 ΔH ≈ ΣE(断裂的键) – ΣE(形成的键)。此式适用于气体；若涉及液态或固态须额外考虑状态变化。
ΔH ≈ ΣE(broken) – ΣE(formed)
9. Equilibrium Constant Kc | 平衡常数 Kc
For a homogeneous reaction aA + bB ⇌ cC + dD, the equilibrium constant in terms of concentration is:
对于均相反应 aA + bB ⇌ cC + dD，用浓度表示的平衡常数为：
Kc = [C]ᶜ [D]ᵈ / ([A]ᵃ [B]ᵇ)
Kc expression includes only aqueous and gaseous species; pure solids and liquids are omitted because their concentrations are constant. Kc changes only with temperature.
Kc 表达式仅包含溶液和气态物种；纯固体和纯液体浓度恒定故不写入。Kc 值仅随温度变化。
10. pH and Strong Acids & Bases | pH 与强酸强碱
pH is defined as the negative logarithm to base 10 of the hydrogen ion concentration.
pH 定义为氢离子浓度的负对数（以 10 为底）。
pH = –log₁₀[H⁺]
To find [H⁺] from a known pH, use [H⁺] = 10⁻ᵖᴴ.
由已知 pH 求 [H⁺] 时用 [H⁺] = 10⁻ᵖᴴ。
For strong monoprotic acids like HCl, [H⁺] equals the acid concentration. For strong bases like NaOH, [OH⁻] equals the base concentration (multiplied by the number of OH⁻ ions per formula unit); then use Kw to find [H⁺] and pH.
像 HCl 这类强一元酸，[H⁺] 等于酸的浓度。对于 NaOH 等强碱，[OH⁻] 等于碱浓度（乘以每分子 OH⁻ 数）；再借助 Kw 求出 [H⁺] 和 pH。
11. Ionic Product of Water Kw | 水的离子积 Kw
Water self-ionises slightly: 2H₂O ⇌ H₃O⁺ + OH⁻. The ionic product Kw is defined as:
水微弱自耦电离：2H₂O ⇌ H₃O⁺ + OH⁻。离子积 Kw 定义为：
Kw = [H⁺][OH⁻]
At 25 °C, Kw = 1.0 × 10⁻¹⁴ mol² dm⁻⁶. Kw increases with rising temperature because the auto-ionization is endothermic.
25 °C 时 Kw = 1.0 × 10⁻¹⁴ mol² dm⁻⁶。Kw 随温度升高而增大，因为水的自耦电离吸热。
In pure water at 25 °C, [H⁺] = [OH⁻] = √Kw = 1.0 × 10⁻⁷ mol dm⁻³, hence pH = 7.
在 25 °C 纯水中，[H⁺] = [OH⁻] = √Kw = 1.0 × 10⁻⁷ mol dm⁻³，因此 pH = 7。
12. Key Constants & Unit Conversions | 关键常数与单位换算
Keep these essential constants and conversions on hand for all calculations.
以下关键常数和单位换算应随时掌握。
| Constant / Conversion | Value |
| Avogadro constant, Nₐ | 6.022 × 10²³ mol⁻¹ |
| Gas constant, R | 8.31 J mol⁻¹ K⁻¹ |
| Molar volume at RTP | 24.0 dm³ mol⁻¹ (20 °C, 1 atm) |
| Standard pressure | 1 atm = 101 325 Pa |
| Specific heat capacity of water | 4.18 J g⁻¹ °C⁻¹ |
| Kw at 25 °C | 1.0 × 10⁻¹⁴ mol² dm⁻⁶ |
| Temperature conversion | K = °C + 273 |
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