问题 选择题

下列各组物质在不同条件下反应时,均能得到不同产物,其中主要是由温度不同而引起的是(  )

①Na+O2   ②P+Cl2   ③C2H5OH+H2SO4 (浓)   ④Cu+HNO3    ⑤CO2+NaOH   ⑥C2H2+HCl    ⑦Fe+H2SO4   ⑧Cl2+NaOH.

A.①③⑧

B.②⑤⑦

C.③④⑧

D.②③⑥

答案

①钠和氧气常温下生成氧化钠,点燃条件反应生成过氧化钠,故①符合;

②氯气和磷的反应与氯气的量有关,可以生成三氯化磷和五氯化磷,故②不符合;

③乙醇在浓硫酸作用下140°C生成乙醚,170°C生成乙烯,故③符合;

④铜和稀硝酸反应生成一氧化氮,与浓硝酸反应生成二氧化氮,故④不符合;

⑤二氧化碳与氢氧化钠反应量少生成碳酸钠,二氧化碳过量会生成碳酸氢钠,故⑤不符合;

⑥乙炔和氯化氢加成反应,氯原子可以接在一个碳上也可以接在两个碳原子上,故⑥不符合;

⑦铁与稀硫酸反应生成硫酸亚铁和氢气,常温下浓硫酸中 钝化,故⑦不符合;

⑧氯气和氢氧化钠溶液反应通常条件下反应生成氯化钠次氯酸钠和水,加热条件下生成氯化钠氯酸钠和水,故与温度有关,故⑧符合;

综上所述:①③⑧符合;

故选A.

问答题
阅读理解

阅读理解。

     It doesn't make any difference how long your speech is. Unless you tune in the first 60 seconds, the

chances are they will tune you out.   

     Take the fellow who opens: "On my way over to the club tonight, I ran into a bum (流浪汉) who asked

me for $ 49.50 for a cup of coffee. I told him he'd do much better if he asked for a quarter. He said, 'Do

you think I'm going into the Ritz in these clothes?'" We know his purpose: to win his audience over with

humor. His bit of humor, however, has no connection with his speech. He has his audience laughing at the

wrong time. Once you have an audience laughing it's hard to get them to switch to an entirely different train

of thought. There is nothing wrong with humor in a speech as long as it has something to do with the purpose

of his speech. To open a speech with humor just to be entertaining invites an almost sure"turnoff" for the

remainder of the talk.  

1. What, in a speech, determines its failure or success?   

A. The purpose of the speech.     

B. A sense of humor.   

C. The opening remarks.       

D. A forceful ending.  

2. If a speaker decides to be humorous, his humor should _________.   

A. be connected with his subject      

B. make his audience laugh   

C. be fresh and different          

D. be reserved for the end  

3. What do the underlined words mean?   

A. bring your speech to an end

B. cause your audience to lose interest   

C. make your audience go away at once

D. have your audience laugh with you  

4. Which of the following best expresses the main idea of the passage?  

A. The opening part of your speech should not be long.   

B. Humor is important in the success of your speech.   

C. Your humor should be relevant (相关的) and timely.   

D. An outstanding speech is full of jokes.