定义Definition
置换反应是一种单质与一种化合物反应，生成另一种单质和另一种化合物的反应（A + BC → AC + B）。它属于氧化还原反应，是中学化学四种基本反应类型之一。
A single displacement reaction is one in which an element reacts with a compound to give another element and another compound (A + BC → AC + B). It is a redox reaction and one of the four basic reaction types in school chemistry.
金属活动性顺序Activity series
K > Ca > Na > Mg > Al > Zn > Fe > Sn > Pb > (H) > Cu > Hg > Ag > Pt > Au。排在前面的金属能把后面的金属从其盐溶液中置换出来；排在 H 前的金属能置换稀酸中的氢。K、Ca、Na 先与水反应，不能直接置换盐溶液中的金属。
K > Ca > Na > Mg > Al > Zn > Fe > Sn > Pb > (H) > Cu > Hg > Ag > Pt > Au. A metal displaces those after it from salt solutions; metals before H displace hydrogen from dilute acids. K, Ca and Na react with water first instead of displacing metals.
本质Underlying chemistry
活动性顺序本质上反映标准电极电势：E°(Mⁿ⁺/M) 越负，金属越易失电子。卤素之间也有置换：Cl₂ > Br₂ > I₂（Cl₂ + 2KBr → 2KCl + Br₂）。
The series reflects standard electrode potentials: the more negative E°(Mⁿ⁺/M), the more readily the metal gives up electrons. Halogens displace each other too: Cl₂ > Br₂ > I₂.
应用Applications
湿法炼铜（铁置换硫酸铜中的铜，中国宋代已用“胆水浸铜”）；铝热反应（Al 置换 Fe₂O₃ 中的铁，用于焊接铁轨）；锌与稀硫酸制氢气。
Hydrometallurgical copper (iron displacing copper from CuSO₄, used in Song-dynasty China); the thermite reaction (Al reducing Fe₂O₃, for welding rails); zinc and dilute sulfuric acid to make hydrogen.
反应Reactions
A 比 B 活泼（还原性更强）
A must be more reactive (a stronger reductant) than B
活泼单质失去（或得到）电子。
The more reactive element transfers electrons.
化合物中的元素被还原（或氧化）成单质析出。
The element in the compound is reduced (or oxidised) and released.
湿法炼铜。
Copper by displacement.
实验室制氢。
Laboratory hydrogen.
年表Timeline
- 11th c.
宋代胆铜法（铁置换铜）工业化
Song-dynasty copper production by iron displacement
- 1895
戈尔德施密特发明铝热法
Goldschmidt invents the thermite process