Perturbations in emitted sound waves c ships are

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Unformatted text preview: anical 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. 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 wells, the height of which remains 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 barrier between the two wells. Recently researchers have developed the concept of tunneling temperature: the temperature belo w 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: the formation of rather complex organic molecules in the deep cold of outer space, where temperatures usually reach only a few degrees Kelvin. Cosmic rays (high-energy protons and other particles) might trigger the synthesis of simple 182 2.According to the passage, classical chemical reactions and 4.Which of the following best describes the hypothesis tunneling reactions are alike in which of the following of Hoyle and Wickramasinghe as it is presented in the ways? passage? (A) In both types of reactions, reacting molecules have to rise (A) Cosmic rays can directly synthesize complex o ver the barrier between the two wells. organic molecules. (B) In both types of reactions, a transition is made from (B) The galactic clouds are the places where prebio- the bottom of one potential well to the bottom of logical evolution of compounds necessary to life another. occurred. (C) In neither type of reaction does the height of the (C) Interstellar formaldehyde can be synthesized by barrier between the wells remain constant. tunneling. (D) In neither type of reaction does the rate of a chemical (D) Molecules of interstellar formaldehyde can evolve reaction depend on its activation energy. into complex organic molecules. (E) In both types of reactions, reacting molecules are able (E) Complex organic molecules can be synthesized to go through the barrier between the two wells. from stable polysaccharides such as cellulose and starch. 3.The author's hypothesis concer...
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This document was uploaded on 09/16/2013.

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