定义Definition
化学计量学研究化学反应中反应物与生成物之间的定量关系。依据是质量守恒和配平的化学方程式：方程式中的系数之比等于参加反应的各物质的物质的量之比。
Stoichiometry deals with the quantitative relationships between reactants and products in chemical reactions. It rests on conservation of mass and the balanced equation: the ratio of coefficients equals the ratio of amounts of the substances that react.
计算步骤Method
写出并配平化学方程式；把已知量换算成物质的量；按系数比求出所需物质的物质的量；再换算成质量、气体体积或浓度。例：完全燃烧 8.0 g CH₄（0.50 mol），CH₄ + 2O₂ → CO₂ + 2H₂O，需 O₂ 1.0 mol（32 g），生成 CO₂ 0.50 mol（22 g）。
Write and balance the equation; convert the known quantity to an amount; use the coefficient ratio to find the amount wanted; convert to mass, gas volume or concentration. Example: burning 8.0 g of CH₄ (0.50 mol), CH₄ + 2O₂ → CO₂ + 2H₂O, needs 1.0 mol (32 g) of O₂ and gives 0.50 mol (22 g) of CO₂.
限量试剂与产率Limiting reagent and yield
反应物不按计量比投料时，先耗尽的为限量试剂，它决定理论产量，另一种过量。实际产量通常低于理论产量，产率 = 实际产量 ÷ 理论产量 × 100%。原子经济性衡量目标产物占全部生成物的比例。
When reactants are not in the stoichiometric ratio, the one used up first is the limiting reagent and fixes the theoretical yield; the other is in excess. The actual yield is usually less, and percentage yield = actual ÷ theoretical × 100%. Atom economy measures how much of the products is the desired one.
年表Timeline
- 1789
拉瓦锡阐明质量守恒定律
Lavoisier sets out the law of conservation of mass
- 1792
里希特提出 stoichiometry 一词，研究酸碱的当量关系
Richter coins the term stoichiometry in his work on equivalent amounts of acids and bases
- 1799
普鲁斯特提出定比定律
Proust states the law of definite proportions
相关公式Formulas
例题Worked example
12 g 碳在 32 g 氧气中完全燃烧，生成 CO₂ 的质量为 12 + 32 = 44 g。
12 g of carbon burning completely in 32 g of oxygen gives 12 + 32 = 44 g of CO₂.