The Sequence of Steps · 步骤序列
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| rate-determining step/reɪt dɪˈtɜːmɪnɪŋ step/ | 决速步 | jué sù bù |
The slowest link sets the pace
- A chain of tasks is only as fast as its slowest one.
- A reaction's steps are the same -- one drags its feet.
- That slowpoke controls how fast the whole thing goes.
- Speed up the fast steps and nothing changes.
最慢的一环决定节奏
- 一连串任务的快慢只取决于其中最慢的那一个。
- 反应的步骤也一样——总有一步拖后腿。
- 那个慢家伙控制着整件事进行得多快。
- 加快那些快步骤,什么也不会改变。
The rate-determining step
- The rate-determining step 决速步 is the slowest elementary step.
- It is the bottleneck of the whole mechanism.
- The overall rate can go no faster than this step.
决速步
- 决速步是最慢的基元反应。
- 它是整个机理的瓶颈。
- 总速率不可能比这一步更快。
The rate-determining step is the... · 决速步是...
The slowest step is the bottleneck controlling the overall rate. · 最慢的步骤是控制整体速率的瓶颈。
The overall reaction can go no faster than its ____ step. · 总反应的速率不能超过其____步骤。
The slowest (rate-determining) step caps the overall rate. · 最慢的（决速）步骤限制了整体速率。
The rate law follows it
- The overall rate law comes from the slowest step's reactants.
- A step's own coefficients are its orders, unlike the overall reaction.
- So the mechanism predicts the experimental rate law.
速率方程跟随它
- 总速率方程来自最慢步骤的反应物。
- 一个步骤自己的系数就是它的级数,这与总反应不同。
- 所以机理能预测实验的速率方程。
For a slow step $A + A \to C$, the rate law is... · 对于慢步骤$A + A \to C$，速率方程为...
Two A's collide in the slow step, giving second order in A. · 两个A在慢步骤中碰撞，导致对A呈二级反应。
For an elementary step, the coefficients can be used as the reaction orders. · 对于基元步骤，可以使用系数作为反应级数。
This is only valid for elementary steps, not overall reactions. · 这只适用于基元步骤，不适用于总反应。
Fast steps barely matter
- Steps after the slow one do not affect the rate.
- Speeding up a fast step leaves the overall rate unchanged.
- Only the bottleneck matters.
快步骤几乎无关紧要
- 慢步骤之后的步骤不影响速率。
- 加快一个快步骤,总速率保持不变。
- 只有瓶颈才重要。
The rate-determining step · 决速步
Follow a two-step mechanism and spot the slow step that controls the rate. · 跟踪两步机理，找出控制速率的慢步骤。
Speeding up a fast step that is not the bottleneck changes the overall rate. · 加快非瓶颈的快速步骤不会改变整体速率。
Only the slowest step controls the rate. · 只有最慢的步骤控制速率。
Slow step: $A + A \to C$. Fast step: $C + B \to D$.
- The slow step's reactants are two A's.
- So $\text{rate} = k[A]^2$, set entirely by the slow step.
慢步骤:$A + A \to C$。快步骤:$C + B \to D$。
- 慢步骤的反应物是两个 A。
- 所以 $\text{rate} = k[A]^2$,完全由慢步骤决定。
The experimental rate law is best predicted from... · 实验速率方程最好从...预测
The slowest step's reactants set the rate law. · 最慢步骤的反应物决定了速率方程。
The rate law comes from the rate-determining (slowest) step, not from the overall balanced equation. A step's coefficients give its orders only because it is elementary. And speeding up a step that is not the bottleneck will not speed the reaction.
速率方程来自决速(最慢)步骤,而不是总的配平方程。一个步骤的系数给出它的级数,仅仅因为它是基元的。而且加快一个不是瓶颈的步骤,不会加快反应。
The rate-determining step is the slowest elementary step, and it sets the overall rate and rate law. Because it is elementary, its coefficients are its orders. Faster steps before or after it do not change the pace -- only the bottleneck does.
决速步是最慢的基元反应,它决定总速率和速率方程。因为它是基元的,它的系数就是它的级数。它之前或之后更快的步骤都不改变节奏——只有瓶颈才改变。