问题 选择题

一定条件下,合成氨反应达到平衡时,测得混合气体中氨气的体积分数为20.0%,与反应前的体积相比,反应后体积缩小的百分率是

A.80.0%

B.20.0%

C.16.7%

D.83.3%

答案

答案:C

解:由合成氨的化学反应达到平衡时,测得混合气体中氨气的体积分数为20.0%,

设平衡时气体总体积为100L,则氨气为100L×20%=20L,

气体缩小的体积为x,则

N2+3H2?2NH3      △V

1   3    2        2

20L      x

=

解得x=20L,

原混合气体的体积为100L+20L=120L,

反应后体积缩小的百分率为×100%=16.7%,

故选:C

阅读理解

If you want to find out a piece of information about anything, the best place to search for it is Wikipedia. This online encyclopedia(百科全书) is written by thousands of people around the world. Anyone can add or change the information if he or she finds it not correct or not well written. In this way, people who know a lot about a certain subject can write about it even if they are not university professors.

What is more, Wikipedia includes articles written in about 235 languages. This fact makes it one of the few websites on the Internet that are truly international. It was started in 2001 by Larry Sanger and Jimmy Wales, as a free online English-language encyclopedia project. By April 2008 over 10 million articles had been put on Wikipedia. A quarter of the articles in English. Wikipedia is also a place where people can find the latest news.

However, Wikipedia has its own problems. There have been many complaints that some of the information on Wikipedia is not accurate and some important subjects are not included. This has led to arguments between the writers of articles. The people running Wikipedia say that the accuracy of the information is improving and that it is one of the top 20 visited websites on the Internet.

So, if you are looking for some information, why not try Wikipedia?

小题1:Wikipedia is ___________.

A.a computer game

B.an online magazine

C.a free university

D.a website encyclopedia小题2:People who write on Wikipedia__________.

A.know much about a certain subject

B.likes writing different stories

C.can’t be university professors

D.are usually famous scientists小题3:The underlined word “accurate” means __________.

A.错误的

B.准确的

C.有条理的

D.逻辑的小题4:Which is TRUE according to the passage?  

A.Wikipedia includes articles written in about 253 languages.

B.People can find information about different subjects on Wikipedia.

C.Wikipedia is the only truly international website on the Internet.

D.Half of the articles on Wikipedia are written in English.

选择题