Year 12 WJEC Chemistry: Formula and Theorem Quick Reference Handbook | WJEC 12年级化学：公式定理速查手册

📚 Year 12 WJEC Chemistry: Formula and Theorem Quick Reference Handbook | WJEC 12年级化学：公式定理速查手册

This quick reference handbook brings together all the essential formulae, equations and quantitative relationships needed for the WJEC Year 12 Chemistry specification. Use it to reinforce your understanding, check calculations and build confidence before assessments. Each section pairs a concise English explanation with Chinese translation, followed by the key formula presented in bold centred style.

本速查手册汇集了 WJEC 12 年级化学课程所需的所有重要公式、方程和定量关系。用它来巩固理解、检查计算并在评估前建立信心。每一节都先给出简洁的英文说明与中文翻译，随后用加粗居中格式呈现核心公式。

---

1. Mole Calculations | 摩尔计算

The mole is the counting unit of chemistry, linking mass, solution concentration and gas volumes. The amount of substance n can be found from mass, from the volume and concentration of a solution, or from the volume of a gas at room temperature and pressure (RTP).

摩尔是化学中的计数单位，将质量、溶液浓度和气体体积联系起来。物质的量 n 可以通过质量、溶液的体积与浓度或在常温常压 (RTP) 下气体的体积求得。

n = m / M
n = c × V
n = V(gas) / 24 (at RTP)

Here m is mass in g, M is molar mass in g mol⁻¹, c is concentration in mol dm⁻³, V is volume in dm³. At RTP (20 °C and 1 atm) one mole of any gas occupies 24 dm³, so dividing the measured gas volume in dm³ by 24 gives the number of moles.

其中 m 为质量 (g)，M 为摩尔质量 (g mol⁻¹)，c 为浓度 (mol dm⁻³)，V 为体积 (dm³)。在 RTP（20 °C、1 atm）下，1 摩尔任何气体的体积约为 24 dm³，因此将测得的气体体积 (dm³) 除以 24 即可得到物质的量。

---

2. Ideal Gas Equation | 理想气体方程

When gases do not behave ideally the mole calculation above is only approximate. The ideal gas equation links pressure, volume, temperature and amount exactly, provided the correct units are used.

当气体行为不理想时，上述摩尔计算仅为近似。理想气体方程将压强、体积、温度与物质的量精确关联，前提是使用正确的单位。

pV = nRT

where p is pressure in pascals (Pa), V is volume in cubic metres (m³), n is moles, R is the gas constant 8.31 J mol⁻¹ K⁻¹, and T is the absolute temperature in kelvin (K). To convert °C to K, add 273. Always check that volume is in m³ (1 m³ = 1000 dm³) and pressure is in Pa (1 kPa = 1000 Pa).

其中 p 为压强 (Pa)，V 为体积 (m³)，n 为物质的量，R 为气体常数 8.31 J mol⁻¹ K⁻¹，T 为热力学温度 (K)。摄氏温度转开尔文需加 273。务必注意体积单位要转换为 m³（1 m³ = 1000 dm³），压强用 Pa（1 kPa = 1000 Pa）。

---

3. Enthalpy Changes | 焓变计算

Enthalpy change, ΔH, is measured by recording the temperature change of a known mass of solution and then dividing the heat exchanged by the number of moles that react.

焓变 ΔH 的测定方法是记录已知质量溶液的温度变化，然后将交换的热量除以反应的物质的量。

q = m × c × ΔT
ΔH = –q / n (exothermic)
ΔH = +q / n (endothermic)

In calorimetry, q is the heat energy in joules, m is the mass of the solution (assume 1 cm³ ≈ 1 g for dilute aqueous solutions), c is the specific heat capacity (4.18 J g⁻¹ °C⁻¹ for water), and ΔT = T(final) – T(initial). For exothermic reactions where the temperature rises, ΔH is negative; for endothermic reactions where the temperature falls, ΔH is positive. The result can be converted to kJ mol⁻¹ by dividing by 1000.

在量热实验中，q 为热量 (J)，m 为溶液质量（稀水溶液可按 1 cm³ ≈ 1 g 处理），c 为比热容（水为 4.18 J g⁻¹ °C⁻¹），ΔT = 最终温度 – 初始温度。对于温度升高的放热反应，ΔH 取负值；对于温度降低的吸热反应，ΔH 取正值。结果除以 1000 即可转换为 kJ mol⁻¹。

---

4. Reaction Kinetics | 反应动力学

The rate of a chemical reaction is defined as the change in concentration of a reactant or product per unit time. In WJEC calculations, rate is usually expressed in mol dm⁻³ s⁻¹.

化学反应速率定义为单位时间内反应物或产物浓度的变化。在 WJEC 的计算中，速率通常以 mol dm⁻³ s⁻¹ 表示。

rate = –Δ[reactant] / Δt = Δ[product] / Δt

The minus sign ensures that the rate remains positive when the reactant concentration decreases. Δ[reactant] and Δ[product] are the concentration changes (mol dm⁻³) over the time interval Δt (s). The rate can be determined from the gradient of a concentration–time graph at a specific time.

负号是为了在反应物浓度下降时保证速率值为正。Δ[reactant] 和 Δ[product] 为在时间间隔 Δt (s) 内的浓度变化 (mol dm⁻³)。速率可通过浓度–时间图在某时刻的切线斜率求得。

---

5. Chemical Equilibrium Constants | 化学平衡常数

For a reversible reaction at equilibrium at a given temperature, the ratio of product concentrations to reactant concentrations, each raised to the power of its stoichiometric coefficient, is constant.

对于给定温度下达到平衡的可逆反应，产物浓度与反应物浓度的比值（各自以其化学计量系数为指数）是一个常数。

5a. Kc – the equilibrium constant in terms of concentration

For the general reaction aA + bB ⇌ cC + dD, the equilibrium constant Kc is expressed using equilibrium concentrations in mol dm⁻³.

对于一般反应 aA + bB ⇌ cC + dD，平衡常数 Kc 使用平衡浓度 (mol dm⁻³) 表示。

Kc = [C]ᶜ [D]ᵈ / [A]ᵃ [B]ᵇ

The units of Kc depend on the sum of the powers in the numerator and denominator and must be derived for each reaction.

Kc 的单位取决于分子和分母中指数之和，需根据具体反应推导。

5b. Kp – the equilibrium constant in terms of partial pressure

For gaseous equilibria

Published by TutorHao | Year 12 Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）