Section outline

  • General

    Collapse all Expand all

  • 不可逆反应

    A bright flame rising against a black background, symbolizing fire and its effects.

    Where’s the fire?
    ::火灾在哪里?

    Fires are a part of life. Some fires clear the land and allow new growth. Other fires provide warmth on a cold night. Unfortunately, many fires are destructive, leaving damage in their wake. All fires leave changed, never to revert back to the original situation. The carbon dioxide and water generated by a fire go off into the atmosphere and do not return. The change is permanent and irreversible.
    ::火灾是生命的一部分。 有的火灾使土地消失,有的火灾允许新的生长。 有的火灾在寒冷的夜晚提供温暖。 不幸的是,许多火灾是破坏性的,在火灾后留下破坏。所有的火灾都改变了,不再回到原来的状态。火灾产生的二氧化碳和水会进入大气层,不再返回。变化是永久的,是不可逆转的。

    Going to Completion
    ::即将完成至完成

    When one of the products of a reaction is removed from the system as soon as it is produced, the reverse reaction cannot establish itself and equilibrium is never reached. Reactions such as these are said to go to completion. These processes are often referred to as non-reversible reactions . Reactions which go to completion tend to produce one of three types of products: (1) an insoluble precipitate , (2) a , (3) a molecular such as water. Examples of these reactions are shown below.
    ::当一种反应的产品一旦产生就从系统中删除时,反向反应无法自我确定,而且从未达到平衡,据说这种反应会最终完成,这些过程通常被称为不可逆反应,完成反应往往会产生三种产品中的一种sad1)不可溶解的沉淀剂,(2)a,(3)分子,如水,这些反应的例子见下文。

    1. Formation of a precipitate
      ::仓促剂的形成

    AgNO 3 ( a q ) + NaCl ( a q ) → NaNO 3 ( a q ) + AgCl ( s )
    ::AGNO3(aq)+NaCl(aq)+NaNO3(aq)+AgCl(s)

    1. Formation of a gas
      ::气体的形成

    Mg ( s ) + 2 HCl ( a q ) → MgCl 2 ( a q ) + H 2 ( g )
    ::Mg(s)+2HCl(aq)MgCl2(aq)+H2(g)

    1. Formation of water
      ::水的形成

    HCl ( a q ) + NaOH ( a q ) → NaCl ( a q ) + H 2 O ( l )
    ::HCl(aq) + NaOH(aq) + NaCl(aq)+H2O(l)

    If we look at these reactions in more detail, we can see some things that are not apparent the way the equations are written. Looking at the first equation, we do not see a double arrow between reactants and products because the reaction is considered essentially irreversible. However if we consider the net ionic equation Ag + + Cl − → AgCl , then the reverse reaction would be AgCl → Ag + + Cl − . The  K e q for the reverse reaction is 1.8 × 10 -10 . For all practical purposes, the reaction goes to completion.
    ::如果我们更详细地研究这些反应, 我们就能看到一些不明显的方程式的写法。 看第一个方程式, 我们看不到反应器和产品之间的双箭, 因为反应基本上被认为是不可逆转的。 但是, 如果我们考虑净离子方程式 Ag++ClAggCl, 那么反向反应就是 AgClAg+Cl-。 反向反应的Keq是1.8 × 10- 10。 为了所有实际目的, 反向反应是完成的 。

    Formation of a gas in an open system is essentially irreversible since the gas escapes into the atmosphere. Looking at the we see that Mg is much higher in the series than hydrogen. So the reaction would be expected to go strongly in the indicated direction.
    ::气体在开放系统中的形成基本上是不可逆转的,因为气体会从大气中渗入。看看我们看到Mg在序列中比氢含量高得多。因此,预计反应会强烈地朝着指示的方向发展。

    The third reaction gets a little more complicated. In solution, the reactants HCl and NaOH will be ionize completely as does the NaCl product. Water exists in an equilibrium with H + and OH - , with the constant for water being 1 × 10 -14 . So, in the solution resulting from the reaction given here, the [H + ] is 1 × 10 -7  M, a very insignificant amount. For all practical purposes, this reaction can be said to go to completion.
    ::第三个反应变得更加复杂。 在解决方案中, HCl 和 NaOH 反应剂将和 NaCl 产品一样完全离子化。 水存在于H+ 和 OH- 的平衡中, 水的常数为 1 × 10-14 。 因此, 在此处给出的反应产生的解决方案中, [H+] 是 1 × 10-7 M, 数量非常小。 为了所有实际目的, 这种反应可以说是完成的 。

     

     

    Summary
    ::摘要

    • Non-reversible reactions are those that go to completion.
      ::不可逆的反应是那些即将完成的反应。

    Review
    ::回顾

    1. List the three situations for non-reversible reactions.
      ::列出三种不可逆反应的情况。
    2. Silver nitrate also forms a precipitate with NaI. What would this precipitate be?
      ::硝酸银也与纳伊尔形成关系。
    3. Would the reaction between HBr and KOH also be considered irreversible?
      ::HBR和KOH之间的反应是否也被认为是不可逆转的?