章节大纲

  • A hazy view of a city skyline with a bridge over a river.

    Where did the sun go?
    ::太阳到哪里去了?

    Gasoline-powered vehicles emit a lot of harmful materials. Nitrogen oxides are formed when atmospheric nitrogen reacts with oxygen at the high temperatures found in a car engine. Carbon monoxide is a by-product of incomplete combustion of . Evaporated and unused fuel releases volatile hydrocarbons into the atmosphere to help form smog. The presence of a catalytic converter in the exhaust system of the car causes these materials to react and be changed into less harmful products.
    ::气动汽车排放大量有害材料。当大气氮在汽车发动机的高温下与氧发生反应时,氮氧化物会形成。一氧化碳是不完全燃烧的副产品。蒸发和未使用的燃料将挥发性碳氢化合物释放到大气中,帮助形成烟雾。汽车排气系统中的催化转换器的存在使这些材料产生反应,并变成危害较小的产品。

    Catalysts
    ::催化器

    Sometimes a substance can be added to a and it will cause that reaction to undergo a dramatic increase in rate. Hydrogen peroxide is used as a disinfectant for scrapes and cuts and is found in many medicine cabinets as a 3% aqueous solution . Hydrogen peroxide naturally decomposes to produce water and oxygen , but the reaction is very slow. A bottle of hydrogen peroxide will last for several years before it needs to be replaced. However, the addition of just a small amount of manganese(IV) oxide to hydrogen peroxide will cause it to decompose completely in just a matter of minutes. A catalyst is a substance that increases the rate of a chemical reaction by lowering the without being used up in the reaction. After the reaction occurs, a catalyst returns to its original state and so catalysts can be used over and over again. Because it is neither a reactant nor a product, a catalyst is shown in a chemical equation by being written above the yield arrow.
    ::有时一种物质可以添加到一种物质中,它会导致这种反应的速率急剧上升。 氢过氧化氢被用作消毒剂用于消毒和切削,并且在许多药柜中作为3%的水溶液被发现。 氢过氧化氢自然分解产生水和氧,但反应非常慢。 一瓶氢过氧化氢在需要替换之前会持续几年。 然而,在过氧化氢中添加少量锰(IV)氧化物,会使其在几分钟内完全分解。 催化剂是一种物质,通过降低化学反应的速度,而不在反应中使用。 反应发生后,催化剂会恢复到原来的状态, 催化剂可以反复使用。 由于它既不是反应剂,也不是产品, 催化剂会通过写在产出箭上而在一个化学方程式中显示。

    2 H 2 O 2 ( a q ) MnO 2 ⟶ 2 H 2 O ( l ) + O 2 ( g )


    ::2H2O2(aq) MnO22H2O(l)+O2(g)

    A catalyst works by changing the specific way in which the reaction occurs, called its mechanism. The important outcome from the use of a catalyst is that the overall activation energy of the reaction is lowered (see Figure ). With a lower activation energy barrier, a greater percentage of reactant molecules are able to have effective collisions and the increases.
    ::通过改变反应发生的具体方式,即其机制,催化作用发挥作用。使用催化剂的重要结果是降低反应的总体活化能量(见图 )。随着活化能量屏障的降低,反应分子中能够发生有效碰撞和增加的反作用分子比例更高。

    Graph comparing activation energy of uncatalyzed and catalyzed chemical reactions.

    The addition of a catalyst to a reaction lowers the activation energy, increasing the rate of the reaction. The activation energy of the uncatalyzed reaction is shown by Ea, while the catalyzed reaction is shown by Ea’. The heat of reaction (ΔH) is unchanged by the presence of the catalyst.
    ::在反应中添加催化剂会降低激活能量,提高反应速度。 Ea显示了未催化反应的激活能量,Ea则显示了催化反应的激活能量。 反应热(H)因催化剂的存在而保持不变。

    Catalysts are extremely important parts of many chemical reactions. in your body act as nature’s catalysts, allowing important biochemical reactions to occur at reasonable rates. Chemical companies constantly search for new and better catalysts to make reactions go faster and thus make the company more profitable.
    ::催化剂是许多化学反应中极为重要的部分。 在你的身体里,催化剂是大自然的催化剂,使得重要的生化反应能够以合理的速率发生。 化学公司不断寻找新的更好的催化剂,让反应更快,从而使公司更有利可图。

     

     

    Summary
    ::摘要

    • The function of a catalyst is described.
      ::说明催化剂的功能。

    Review
    ::回顾

    1. What does a catalyst affect in a chemical reaction?
      ::催化剂在化学反应中影响什么?
    2. Is the  Δ H for the process affected?
      ::过程是否受到影响?
    3. When writing a chemical equation, where do we indicate the catalyst?
      ::当刻写化学方程式时,我们在哪里标明催化剂?

    Explore More
    ::探索更多

    Use the resource below to answer the questions that follow.
    ::利用以下资源回答以下问题。

     

    1. What dye is used on blue jeans?
      ::蓝色牛仔裤用什么染料?
    2. What do enzymes do for the blue jeans?
      ::蓝牛仔裤的酶是做什么的?
    3. List three issues that exist for uncatalyzed reactions.
      ::列出三个问题,供未经催化的反应使用。