节: 中间反应 | 18.12 中间反应

章节大纲

Ozone depletion
::臭氧消耗

Ozone (O ₃ ) depletion in the atmosphere is of significant concern. This serves as a protection against the ultraviolet rays of the sun. Ozone is naturally depleted in addition to the depletion caused by human-made chemicals. The depletion reaction is a two-step process:
::臭氧(O3)在大气中的消耗是一个令人十分关切的问题,它是一种防止太阳紫外线的防护措施,除了人为化学品造成的消耗外,臭氧自然也消耗殆尽。

$\begin{aligned} O_{3} + ultraviolet light \to O_{2} + O \cdot (free radical) slow reaction \\ O \cdot + O_{3} \to 2 O_{2} fast reaction \end{aligned}$
$\begin{align*}& \text{O}_3 + \text{ultraviolet light} \rightarrow \text{O}_2 + {\text{O} \cdot} (\text{free radical}) \ \text{slow reaction} \\ & {\text{O} \cdot} + \text{O}_3 \rightarrow 2 \text{O}_2 \ \text{fast reaction} \end{align*}$
::O3+紫外光光2+O(无自由基)慢反应OO3+紫外光2O2快速反应

The free radical is not a part of the overall equation, but can be detected in the lab.
::自由基不是整体方程的一部分,但可以在实验室中检测到。

Intermediate
::中间中间

Reaction mechanisms describe how the material in a gets from the initial reactants to the final products. One reaction that illustrates a reaction mechanism is the reaction between nitrogen monoxide and oxygen to form nitrogen dioxide:
::反应机制描述一种物质从初始反应器到最终产品是如何从初始反应器到最终产品的。

$\begin{aligned} 2 NO (g) + O_{2} (g) \to 2 {NO}_{2} (g) \end{aligned}$
$\begin{align*}2 \text{NO}(g)+ \text{O}_2(g) \rightarrow 2 \text{NO}_2(g)\end{align*}$
::2NO(g)+O2(g)+O2(g)

It may seem as though this reaction would occur as the result of a collision between two NO molecules with one O ₂ molecule. However, careful analysis of the reaction has detected the presence of N ₂ O ₂ during the reaction. A proposed mechanism for the reaction consists of two elementary steps:
::这种反应似乎是两个NO分子与一个O2分子碰撞的结果。然而,对反应的仔细分析发现,在反应过程中出现了N2O2。

Step 1: $\begin{align*}2 \text{NO}(g) \rightarrow \text{N}_2 \text{O}_2(g)\end{align*}$
::步骤1:2NO(g)N2O2(g)

Step 2: $\begin{align*}\text{N}_2 \text{O}_2(g)+ \text{O}_2(g) \rightarrow 2 \text{NO}_2(g)\end{align*}$
::第2步:N2O2(g)+O2(g)

In the first step, two molecules of NO collide to form a molecule of N ₂ O ₂ . In the second step, that molecule of N ₂ O ₂ collides with a molecule of O ₂ to produce two molecules of NO ₂ . The overall chemical reaction is the sum of the two elementary steps:
::在第一步,两个无相撞分子形成N2O2分子。第二步,N2O2分子与一个O2分子相撞,产生两个NO2分子。总化学反应是两个基本步骤的总和:

$\begin{aligned} 2 NO (g) \to N_{2} O_{2} (g) \\ \underline{N_{2} O_{2} (g) + O_{2} (g) \to 2 {NO}_{2} (g)} \\ 2 NO (g) + O_{2} (g) \to 2 {NO}_{2} (g) \end{aligned}$
$\begin{align*}& \qquad \qquad \ 2 \text{NO} (g) \rightarrow \cancel{\text{N}_2 \text{O}_2(g)} \\ & \underline{\;\; \cancel{\text{N}_2\text{O}_2(g)} + \text{O}_2(g) \rightarrow 2 \text{NO}_2(g) \;\;} \\ & \ \ 2 \text{NO}(g)+ \text{O}_2(g) \rightarrow 2 \text{NO}_2(g)\end{align*}$
::2NO(g)-N2O2(g)-N2O2(g)-N2O2(g)-O2(g)-2NO(g)_2NO(g)-O2(g)-2NO(g)-2(g)-2NO2(g)-2NO2(g)-2(g)

The N ₂ O ₂ molecule is not part of the overall reaction. It was produced in the first elementary step , then reacts in the second elementary step. An intermediate is a species which appears in the mechanism of a reaction, but not in the overall balanced equation . An intermediate is always formed in an early step in the mechanism and consumed in a later step.
::N2O2分子不是整体反应的一部分。它是在初级阶段生产的,然后在初级阶段作出反应。中间体是一种物种,出现在反应机制中,但不是在总体平衡的方程式中。中间体总是在机制的早期形成,然后消化。

Nitrogen dioxide (left) and dinitrogen tetroxide (right).
::氧化氮(左)和四氧化二氮(右)。

Summary
::摘要

The role of intermediates in reaction mechanisms is described.
::介绍了中间体在反应机制中的作用。

Review
::回顾

What is the intermediate in the reaction described above?
::上述反应的中间点是什么?

Do we see this intermediate in the actual reaction mix?
::我们是否在实际反应组合中看到中间点?

Where do we first see an intermediate in the reaction mechanism?
::我们首先在反应机制中在哪里看到中间体?

What happens to the intermediate?
::中间线怎么了?

章节大纲

Ozone depletion ::臭氧消耗

Intermediate ::中间中间

Summary ::摘要

Review ::回顾

Ozone depletion
::臭氧消耗

Intermediate
::中间中间

Summary
::摘要

Review
::回顾