问题 选择题

下列对化学反应方向的叙述,正确的是(  )

A.室温下不能自发进行的反应,在高温下有可能自发进行

B.熵增加有利于反应的自发进行,熵减少的反应常温下都不会自发进行

C.非自发反应在任何情况下都不会发生

D.△H-T△S作为化学反应方向的判据,在任何条件下都适用

答案

A.室温下不能自发进行的反应,如升高温度,使△H-T•△S<0时,有可能自发进行,如碳酸钙的分解,故A正确;

B.熵减少的反应常温下不一定给自发进行,如氨气和HCl的反应,故B错误;

C.非自发反应的反应不一定不能发生,如铜和稀硫酸的反应,可用铜作阳极,硫酸为电解质溶液,用电解法反应可发生,故C错误;

D.反应的自发性是指没有外界干扰式体系的性质,故D错误.

故选A.

选择题
单项选择题

There (1) not one type of reading but several according to your reasons for reading. To read carefully, you have to (2) your reading speed and technique (3) your aim (4) reading. Skimming is a technique necessary for quick and efficient reading.

When skimming, you (5) the reading (6) quickly in order to get the (7) of it, to know how it is organized, (8) an idea of the tone or the intention of the writer. Skimming is (9) an activity which (10) an overall view of the text and (11) a definite reading competence.

Skimming doesn’t need reading all the material, but it doesn’t mean that it is an (12) skill for the lazy, because it need a high degree of alertness and concentration.

When you read, you usually start with (13) understanding and move towards detailed understanding rather than working the other way round. But (14) is also used after you have already carefully studied and you need to (15) the major ideas and concepts.

In order to be able to skim quickly and (16) through a text, you should know where to look for what you want. In preview skimming you read the introductory information, the headings and subheadings, and the summary, if one is provided. (17) this skimming, decide whether to read the material more thoroughly, and select the appropriate speed (18) you read.

The same procedure (19) for preview skimming could also be used to get an overview. Another method would be to read only key words. This is done by omitting the unnecessary words, phrases, and sentences.

In order to skim efficiently and fulfill your purpose, (20) practice is necessary.

12().

A.awful

B.unsuitable

C.ideal

D.wrong