含义Meaning
速率与各反应物浓度幂次之积成正比。级数 m、n 必须由实验确定，一般不等于计量数；只有基元反应的级数等于其分子数（质量作用定律）。
Rate is proportional to a product of concentration powers. Orders must be found by experiment and generally differ from coefficients; only for elementary steps do they equal molecularity (law of mass action).
符号说明Symbols
| 符号Symbol | 含义 Meaning | 单位 Unit |
|---|---|---|
| \(k\) | 速率常数rate constant | （随级数而异） |
| \(m, n\) | 对 A、B 的反应级数orders in A and B | 1 |
推导Derivation
基元反应 A + B → 产物：碰撞频率 ∝ [A][B]，所以 v = k[A][B]（质量作用定律，古德贝格–瓦格，1864）。
For an elementary A + B step collision frequency ∝ [A][B] (law of mass action).
总反应的速率方程由机理决定（决速步、预平衡等），可出现分数或零级。
Overall rate laws follow from mechanisms and can have fractional or zero order.
初速率法：保持其他浓度不变，改变 [A] 观察速率倍数，取对数得 m。
Initial rates: vary [A] alone and compare.
适用条件与局限Assumptions & limitations
速率方程只在一定浓度、温度范围内有效；产物抑制、催化等可使形式更复杂。
Valid over limited ranges; inhibition or catalysis complicates it.
k 的单位随总级数变化：(mol/L)^{1−n}·s⁻¹。
k has units (mol/L)^{1−n} s⁻¹.
例题Worked example
H₂ + Br₂ 的速率方程 v = k[H₂][Br₂]^{1/2}/(1 + k′[HBr]/[Br₂])，说明它是链反应而非基元反应。
H₂ + Br₂ has a complex rate law revealing a chain mechanism.