The Steps a Reaction Really Takes · 反应实际经历的步骤
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| elementary step/ˌelɪˈmentəri step/ | 基元反应 | jī yuán fǎn yìng |
| reaction mechanism/rɪˈækʃn ˈmekənɪzəm/ | 反应机理 | fǎn yìng jī lǐ |
| intermediate/ˌɪntəˈmiːdɪət/ | 中间体 | zhōng jiān tǐ |
The hidden choreography
- A balanced equation shows the start and the finish.
- But reactants rarely leap straight to products in one bound.
- They usually go through a hidden series of small moves.
- That secret sequence is the mechanism.
隐藏的编舞
- 配平的方程显示起点和终点。
- 但反应物很少一跃就直接变成产物。
- 它们通常经过一系列隐藏的小动作。
- 那个秘密的序列就是机理。
Elementary steps
- A reaction mechanism 反应机理 is the real sequence of small steps.
- Each elementary step 基元反应 is a single molecular event.
- Add up the steps and you get the overall reaction.
基元反应
- 反应机理是真实的小步骤序列。
- 每个基元反应是单一的分子事件。
- 把各步骤相加,你就得到总反应。
The elementary steps of a mechanism add up to the overall reaction. · 机理中的基元步骤相加等于总反应方程式。
Summing the steps (cancelling intermediates) gives the overall equation. · 将所有步骤相加（消去中间体）即可得到总反应方程式。
A single molecular event within a mechanism is an ____ step. · 机理内的单个分子事件是一个____步骤。
Each single event is an elementary step. · 每个单独的事件都是一个基元步骤。
Intermediates
- An intermediate 中间体 is made in one step and used up in a later one.
- It does not appear in the overall equation.
- Spot it: it shows up first as a product, then as a reactant.
中间体
- 中间体在一步中生成、在后面一步中被消耗。
- 它不出现在总方程里。
- 认出它:它先作为产物出现,然后作为反应物。
An intermediate is a species that is... · 中间体是一种物种，它...
An intermediate forms then is consumed, so it cancels overall. · 中间体的生成与消耗相互抵消，因此在总反应中不出现。
How many collide
- Molecularity counts how many particles meet in a single step.
- One particle is unimolecular; two is bimolecular.
- Three-particle collisions are rare, so most steps involve one or two.
有几个碰撞
- 反应分子数计算单一步骤中有几个粒子相遇。
- 一个粒子是单分子;两个是双分子。
- 三粒子碰撞很罕见,所以大多数步骤涉及一或两个。
Molecularity of a step · 基元反应的分子数
Classify each elementary step by how many particles must collide. · 根据发生碰撞的粒子数量对每个基元步骤进行分类。
A single step in which two particles collide is called... · 两个粒子碰撞的单一步骤称为...
Two colliding particles make a bimolecular step. · 两个碰撞的粒子构成一个双分子步骤。
Steps requiring three particles to collide at once are common. · 需要三个粒子同时碰撞的步骤很常见。
Three-body collisions are very unlikely, so they are rare. · 三体碰撞非常罕见，因此这类步骤很少见。
Steps: $A + B \to C$ (fast), then $C + B \to D$.
- $C$ is made and then consumed, so it is an intermediate.
- Overall: $A + 2B \to D$, since $C$ cancels out.
步骤:$A + B \to C$(快),然后 $C + B \to D$。
- $C$ 生成后又被消耗,所以它是中间体。
- 总反应:$A + 2B \to D$,因为 $C$ 抵消了。
How does an intermediate differ from a catalyst? · 中间体与催化剂有何区别？
An intermediate appears as a product first; a catalyst appears as a reactant first. · 中间体首先作为产物出现；催化剂首先作为反应物出现。
An intermediate appears then disappears (a product of one step, a reactant of a later one) -- do not confuse it with a catalyst, which appears first as a reactant then reappears. Elementary steps can use their coefficients as orders, unlike the overall reaction. And three-body collisions are so unlikely that real mechanisms avoid them.
中间体先出现后消失(一步的产物、后面一步的反应物)——别把它与催化剂混淆,催化剂先作为反应物出现,然后又重新出现。基元反应可以用它们的系数作为级数,这与总反应不同。而且三体碰撞极不可能,所以真实机理会避免它们。
A reaction mechanism is the sequence of elementary steps that add up to the overall reaction. An intermediate is made in one step and used up later, so it cancels from the overall equation. Molecularity counts the particles meeting in a step -- almost always one or two.
反应机理是相加得到总反应的基元反应序列。中间体在一步生成、后面被消耗,所以从总方程中抵消。反应分子数计算一步中相遇的粒子——几乎总是一个或两个。