2. 外语
  3. About a century ago, the Swedish physical scientist Arrhenius proposed a low of classical chemistry that relates chemical reacti

About a century ago, the Swedish physical scientist Arrhenius proposed a low of classical chemistry that relates chemical reacti

admin2015-01-31  85
问题     About a century ago, the Swedish physical scientist Arrhenius proposed a low of classical chemistry that relates chemical reaction rate to temperature. According to his equation, chemical reactions are increasingly unlikely to occur as temperature approaches absolute zero, and at absolute zero, reactions stop. However, recent experiment evidence reveals that although the Arrhenius equation is generally accurate in describing the kind of chemical reaction that occurs at relatively high temperature, at temperatures closer to zero a quantum-mechanical effect known as tunneling comes into play; this effect accounts for chemical reactions that are forbidden by me principles of classical chemistry. Specifically, entire molecules can tunnel through the barriers of repulsive forces from other molecules and chemically react even though these molecules do not have sufficient energy, according to classical chemistry, to overcome the repulsive barrier.
    The rate of any chemical reaction, regardless of the temperature at which it takes place, usually depends on a very important characteristic known as its activation energy. Any molecule can be imagined to reside at the bottom of a so-called potential well of energy. A chemical reaction corresponds to the transition of a molecule from the bottom of one potential well to the bottom of another. In classical chemistry, such a transition can be accomplished only by going over the potential barrier between the well, the height of which remains constant and is called the activation energy of the reaction. In tunneling, the reactings molecules tunnel from the bottom of one to the bottom of another well without having to rise over the barrier between the two wells. Recently researchers have developed the concept of tunneling temperature: the temperature below which tunneling transitions greatly outnumber Arrhenius transitions, and classical mechanics gives way to its quantum counterpart.
    This tunneling phenomenon at very low temperatures suggested my hypothesis about a cold prehistory of life: formation of rather complex organic molecules in the deep cold of outer space, where temperatures usually reach only a few degrees Kelvin. Cosmic rays might trigger the synthesis of simple molecules, such as interstellar formaldehyde, in dark clouds of interstellar dust. Afterward complex organic molecules would be formed, slowly but surely, by means of tunneling. After I offered my hypothesis, Hoyle and Wickramashinghe argued that molecules of interstellar formaldehyde have indeed evolved into stable polysaccharides such as cellulose and starch. Their conclusions, although strongly disputed, have generated excitement among investigators such as myself who are proposing that the galactic clouds are the places where the prebiological evolution of compounds necessary to life occurred.
Which of the following best describes the organization of the first two paragraphs of the passage?
选项 A、The author cites a basic principle of classical chemistry and then describes the research from which that principle was developed.
B、The author presents the fundamental rules of classical chemistry in order to introduce an explanation of a specific chemical reaction.
C、The author describes the role of heat in chemical reactions and then offers a detailed explanation of its function.
D、The author presents a law of classical chemistry in order to introduce a kind of chemical reaction that differs from it and then explains the essential difference between the two.
答案D
解析 推断题。根据文章前两段内容可知，第一段首先论述了经典化学定理，然后介绍了隧道效应，在第二段中对比经典化学定理和隧道效应，说明二者使用的温度界限不同。和选项D的顺序一致，所以答案选D。
转载请注明原文地址:https://kaotiyun.com/show/ZGh7777K
0

大学英语六级

相关试题推荐
随机试题
最新回复(0)