\[[\mathrm A] = [\mathrm A]_0 - kt,\qquad t_{1/2} = \frac{[\mathrm A]_0}{2k}\]
含义Meaning
速率与浓度无关、保持恒定，浓度随时间线性下降。常见于表面催化（表面饱和）、酶饱和、光化学（光强控制）和缓释药物。
Rate independent of concentration; concentration falls linearly. Typical of saturated surface catalysis, saturated enzymes, light-limited photochemistry and controlled-release drugs.
符号说明Symbols
| 符号Symbol | 含义 Meaning | 单位 Unit |
|---|---|---|
| \(k\) | 零级速率常数zero-order rate constant | mol·L⁻¹·s⁻¹ |
推导Derivation
\(-d[\mathrm A]/dt = k\)，积分 \([\mathrm A] = [\mathrm A]_0 - kt\)。
Integrate \(-d[\mathrm A]/dt = k\).
半衰期与初始浓度成正比。
Half-life ∝ initial concentration.
米氏方程 [S] ≫ K_M 或朗缪尔–欣谢尔伍德 θ ≈ 1 时速率退化为零级。
Michaelis–Menten at [S] ≫ K_M or Langmuir at θ ≈ 1 reduce to zero order.
适用条件与局限Assumptions & limitations
只能是“表观”零级，浓度降低后必然转为其他级数。
Always only apparent; it changes order as reactant runs low.
例题Worked example
NH₃ 在热钨丝上分解、乙醇在肝脏中被乙醇脱氢酶代谢（约 7–10 g/h）近似零级。
NH₃ on hot tungsten and ethanol metabolism in the liver are roughly zero order.