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

admin2010-07-19  51
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 the 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. Some 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 remain constant and is called the activation energy of the reaction. In tunneling, the reacting molecules tunnel from the bottom of one to the bottom of another well without having to rise over the harrier 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 hut 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.
The author is mainly concerned with ______.
选项 A、describing how the principles of classical chemistry were developed
B、initiating a debate about the kinds of chemical reaction required for the development of life
C、explaining how current research in chemistry may be related to broader biological concerns
D、clarifying inherent ambiguities in the laws of classical chemistry
答案C
解析 说明现在化学研究如何能和更广泛的生物学领域有关。最后一段基本上都是谈化学研究与生化的关系。“极低温时的贯穿势垒现象证明我对寒冷的史前生命的假说；在外层空间极其寒冷处，温度一般只有K的几度光景，有相当复杂的有机分子形成。宇宙射线可能激发诸如星际甲醛单分子在星际尘埃的乌云中综合。以后，复杂的有机分子，慢慢地，但稳定地通过贯穿势垒的方式形成。”后又有两位化学家提出“星际甲醛分子确实进化为类似纤维素和淀粉等多糖酶。”他们的结论虽有争议，却实在令人振奋，特别是文章之作者，因为他正提出“拥有巨大云块的这些地方，都曾经存在过生命所必需的前生物进化化合物。”
转载请注明原文地址:https://kaotiyun.com/show/V0lO777K
0

专业英语八级

相关试题推荐
随机试题
最新回复(0)