📚 Mastering Calculations for AQA A-Level Chemistry | AQA A-Level 化学计算全攻略
Calculations are at the heart of AQA A-Level Chemistry. Whether you are working out the number of moles in a reaction, the pH of a buffer, or the enthalpy change of combustion, a systematic approach and careful handling of units will save you marks. This article brings together the core calculation types for AQA A-Level Chemistry, with step-by-step methods, common pitfalls and worked examples.
计算是 AQA A-Level 化学的核心。无论是求反应中的物质的量、缓冲溶液的 pH，还是燃烧反应的焓变，系统的方法和严谨的单位处理都能帮你稳拿分数。本文汇总 AQA A-Level 化学的核心计算类型，提供分步方法、常见陷阱和典型示例。
1. Amount of Substance: The Mole and Molar Mass | 物质的量：摩尔与摩尔质量
gadro constant, Nₐ). The molar mass, Mᵣ, is the mass of one mole of a substance and is given in g mol⁻¹. The key equation linking mass, molar mass and amount in moles is:
摩尔是物质的量的 SI 单位。1 摩尔正好包含 6.022 × 10²³ 个基本单元（阿伏伽德罗常数，Nₐ）。摩尔质量 Mᵣ 是 1 摩尔物质的质量，单位为 g mol⁻¹。联系质量、摩尔质量和物质的量的核心公式为：
n = m / Mᵣ
Always convert mass into grams and molar mass into g mol⁻¹ before substituting. For gases, the molar volume at room temperature and pressure (RTP) is 24.0 dm³ mol⁻¹, and at standard temperature and pressure (STP) it is 22.4 dm³ mol⁻¹. However, AQA normally uses the ideal gas equation for non-RTP conditions.
代入前务必把质量换算为克，摩尔质量换算为 g mol⁻¹。对于气体，常温常压（RTP）下的摩尔体积为 24.0 dm³ mol⁻¹，标准状况（STP）下为 22.4 dm³ mol⁻¹。不过，AQA 在非 RTP 条件下通常使用理想气体状态方程。
for gases. Always state the units and check that the equation is dimensionally consistent.
其他常用关系包括 n = N / Nₐ（N 为粒子数）以及在 RTP 下气体的 n = V / 24.0 dm³ mol⁻¹。务必标明单位并检查方程的量纲是否一致。
2. Empirical and Molecular Formula | 实验式与分子式
The empirical formula shows the simplest whole-number ratio of atoms in a compound. To calculate it, convert the percentage or mass of each element into moles, then divide all mole values by the smallest value to obtain the ratio.
实验式（最简式）表示化合物中各原子的最简整数比。计算方法：将各元素的质量或质量分数换算为物质的量，再用最小物质的量去除所有数值，得到最简整数比。
The molecular formula is a whole-number multiple of the empirical formula. To find it, divide the relative molecular mass (Mᵣ) by the empirical formula mass, then multiply each subscript in the empirical formula by this factor.
分子式是实验式的整数倍。求法：用相对分子质量 Mᵣ 除以实验式质量，然后将实验式中各下标乘以该倍数。
Example: A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% 7 mol, O = 53.3 / 16.0 = 3.33 mol. Dividing each by 3.33 gives the empirical formula CH₂O.
示例：某化合物含 40.0% 碳、6.7% 氢和 53.3% 氧。碳的物质的量 = 40.0 / 12.0 = 3.33 mol，氢 = 6.7 / 1.0 = 6.7 mol，氧 = 53.3 / 16.0 = 3.33 mol。各除以 3.33 得到实验式 CH₂O。
3. Concentration, Dilution and Titration Calculations | 浓度、稀释与滴定计算
V in dm³. For mass concentration, the equation is concentration = mass / volume in g dm⁻³.
浓度是溶解在一定体积溶液中的溶质的量。公式为 c = n / V，其中 c 单位为 mol dm⁻³，n 为 mol，V 为 dm³。质量浓度则用浓度 = 质量 / 体积，单位为 g dm⁻³。
In a titration, you can use the concordant titre to find the unknown concentration. The steps are: write the balanced equation; calculate moles of the known solution; use the mole ratio to find moles of the unknown; finally divide by the volume used.
在滴定中，可用一致的滴定管读数求未知浓度。步骤为：写出配平方程式；计算已知溶液的物质的量；利用摩尔比求出未知物的物质的量；最后除以所用体积。
- Step 1: Write the balanced symbol equation and identify the mole ratio.
- 步骤 1：写出配平的符号方程式，找出摩尔比。
- Step 2: Calculate n(known) = c(known) × V(known in dm³).
- 步骤 2：计算 n(已知) = c(已知) × V(已知，单位 dm³)。
- Step 3: Use the mole ratio to find n(unknown).
- 步骤 3：利用摩尔比求出 n(未知)。
- Step 4: Calculate c(unknown) = n(unknown) / V(unknown in dm³).
- 步骤 4：计算 c(未知) = n(未知) / V(未知，单位 dm³)。
4. Ideal Gas Equation | 理想气体状态方程
ressure, volume, amount and temperature for an ideal gas. p is pressure in Pa, V is volume in m³, n is amount in mol, T is temperature in K, and R is the gas constant 8.31 J K⁻¹ mol⁻¹.
理想气体状态方程 pV = nRT 联系了理想气体的压强、体积、物质的量和温度。p 为压强（Pa），V 为体积（m³），n 为物质的量（mol），T 为热力学温度（K），R 为气体常数 8.31 J K⁻¹ mol⁻¹。
pV = nRT
K = temperature in °C + 273.15. Always rearrange the equation before substituting values.
常见换算：1 kPa = 1000 Pa；1 atm = 101 325 Pa；1 dm³ = 0.001 m³；热力学温度 K = 摄氏温度 + 273.15。代入前应先整理公式。
, where m is the mass of gas in grams. Remember to use the absolute temperature in kelvin.
当要求根据气体数据计算摩尔质量时，将方程整理为 Mᵣ = mRT / pV，其中 m 为气体质量（克）。记住要使用热力学温度开尔文。
5. Enthalpy Changes and Calorimetry | 焓变与量热法
, where m is the mass of water or solution, c is the specific heat capacity (usually 4.18 J g⁻¹ K⁻¹ for water), and ΔT is the temperature change.
反应过程中传递的热量可用 q = mcΔT 计算，其中 m 为水或溶液的质量，c 为比热容（水的比热容通常为 4.18 J g⁻¹ K⁻¹），ΔT 为温度变化。
q = mcΔT
n is the amount in moles of the limiting reagent or the substance specified. Remember to include the sign: exothermic reactions have negative ΔH, endothermic positive.
将热量换算为每摩尔焓变时，使用 ΔH = q / n，其中 n 为限量试剂或指定物质的物质的量。注意符号：放热反应 ΔH 为负，吸热反应为正。
the enthalpy change of combustion is reported per mole of fuel burnt. Divide the heat energy by the moles of fuel to obtain ΔcH with units kJ mol⁻¹.
在燃烧量热法中，q = mcΔT 中的 m 为被加热水的质量，但燃烧焓变以每摩尔燃料计。将热量除以燃料的物质的量，得到 ΔcH，单位为 kJ mol⁻¹。
6. Hess's Law and Born-Haber Cycles | 盖斯定律与玻恩-哈伯循环
Hess's law states that the enthalpy change for a reaction depends only on the initial and final states, not on the route taken. This allows unknown enthalpy changes to be calculated by combining known steps.
盖斯定律指出，反应的焓变只取决于始态和终态，与途径无关。因此可以通过组合已知步骤计算未知焓变。
In Born-Haber cycles, the lattice enthalpy can be determined by combining atomisation enthalpy, ionisation energy, electron affinity and standard enthalpy of formation. Write the cycle carefully, with arrows in the correct direction, and apply Hess's law.
在玻恩-哈伯循环中，晶格焓可通过结合原子化焓、电离能、电子亲和能和标准生成焓求得。画循环图时要仔细标好箭头方向，并应用盖斯定律。
A common method is to set the sum of enthalpy
Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图