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  • General

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  • 反应机制和潜在能源图

    A roller coaster at night, illuminated by lights, showcasing its structure and heights.

    Are roller coasters fun or frightful?
    ::过山车好玩还是吓人?

    For many people, a roller coaster is the epitome of excitement, while for others it is a torture device to be avoided at all costs (and some folks are in-between). For a roller coaster, the rate-limiting step is the climb up to the top at the beginning of the ride, where the cars are hauled slowly to the peak of the ride. This peak must be the highest because the potential energy at this point must be enough to cause the roller coaster to move through the smaller peaks without stopping.
    ::对于许多人来说,过山车是兴奋的缩影,而对于其他人来说,它是一种必须不惜一切代价避免的酷刑装置(有些人在中间 ) 。 对于过山车来说,限制费率的一步就是在车程开始时爬到顶部,汽车被缓慢拖到顶部。 这一峰值必须是最高的,因为目前潜在的能量必须足以让过山车不停地穿过小山峰。

    Potential Energy Diagrams
    ::潜在能源图

    The potential energy diagram can illustrate the mechanism for a reaction by showing each elementary step of the reaction with distinct (see Figure ).
    ::潜在的能量图可以通过显示反应的每一基本步骤和不同的反应来说明反应机制(见图 )。

    Potential energy diagram illustrating activation energy peaks and intermediates in a two-step reaction.

    The potential energy diagram shows an activation energy peak for each of the elementary steps of the reaction. The valley between represents the intermediate for the reaction.
    ::潜在能量图显示了反应每个基本步骤的激活能量峰值。 中间的峡谷代表反应的中间点 。

    The reaction whose potential energy diagram is shown in the figure is a two-step reaction. The activation energy for each step is labeled E a1 and E a2 . Each elementary step has its own , labeled AC 1 and AC 2 . Note that the overall change of the reaction  ( Δ H ) is unaffected by the individual steps, since it depends only on the initial and final states.
    ::图中显示的潜在能量图显示的反应是两步反应。每个步骤的激活能量标有Ea1和Ea2。每个基本步骤都有自己的标有AC1和AC2的标有AC1和AC2。请注意,反应的总体变化不受单个步骤的影响,因为它只取决于初始状态和最终状态。

    In this example, the rate-limiting step in the reaction is the first step, leading to the formation of the activated complex AC 1 . The activation energy is higher for this step than for step two, which has a considerably lower activation energy. If the rate-limiting step were the second step, the peak labeled AC 2 would be higher than the peak for AC 1 and E a2 would be greater than E a1 . The same approach can be taken for a potential energy diagram with more than two peaks.
    ::在这个例子中,反应中的限速步骤是第一步,导致形成活性复合空调1。这一步骤的激活能量比第二步高,第二步的激活能量要低得多。如果降速限制步骤是第二步,标注为AC2的峰值将高于AC1和Ea2的峰值。 对于具有两个以上峰值的潜在能源图,可以采取同样的做法。

     

     

    Summary
    ::摘要

    • A potential energy diagram for a two-step reaction is shown and labeled.
      ::显示并标注了两步反应的潜在能量图。

    Review
    ::回顾

    1. What does a potential energy diagram tell us?
      ::潜在的能量图告诉我们什么?
    2. In the diagram above, which step has the highest activation energy?
      ::在以上图表中,哪个步骤的活性能最高?
    3. If a catalyst lowered the step one activation energy to a value lower than the step two activation energy, which step would be rate-limiting?
      ::如果催化剂将第一步激活能量降低到低于步骤二激活能量的数值,那么哪个步骤是限制率?