问题 问答题

反应4A(s)+3B(g)═2C(g)+D(g),经2min,B的浓度减少了0.6mol/L.对此化学反应速率的正确表示是(  )

A.用A表示的反应速率是0.4mol/(L∙min)

B.分别用B、C、D表示反应的速率,其比值是3:2:1

C.在2min末的反应速率,用B表示是0.3mol/(L∙min)

D.在这2min内B和C物质浓度都逐渐减少

答案

A、物质A是固体,浓度不变,不能用A表示该反应的反应速率,故A错误;

B、速率之比等于化学计量数之比,v(B):v(C):v(D)=3:2:1,故B正确;

C、2min末的反应速率为即时速率,用B表示速率0.3mol/(L∙min),是2min内的平均速率,故C错误;

D、B是反应物,浓度降低,C是生成物,浓度增大,故D错误.

故选B.

阅读理解

     I have been using the Internet since I was five years old, when my dad first sat me down in front of a

computer and connected me the World Wide Web.

     I've always felt like a master(主人) of the Internet world. AOL Instant Messaging, MSN, Gmail,

Facebook. Myspace-I've got it all under control. I thought there was nothing more to it besides checking my e-mail and wasting my time, until I was introduced to electronic commerce(e-commerce): business on

the Internet.

     Some online business are run from one- room home offices. Others have hundreds of employee(雇员)

spread across five different continent. Have you ever heard of Amazon. com, Yahoo. com?

     My friends often said they got cheap textbooks off Amazon.com, or had a good deal(交易)on Steve Madden boots that were on sale at SteveMaden.com. Unfortunately for me, I continued my

"e-commerceless" Web-surfing, unaware(不知道)of all the deals I was missing out on.

     That is, of course, until my sister finally sold the idea to me.

     "Why are all these packages(包裹)arriving in the mail for you, Katy?" I asked her one day. Strange

envelopes had been put on our doorstep for weeks now, each one always addressed to my sister; and we all know little sisters should never be getting more mail than their elders!

     "Oh, it's the things I ordered online!" she answered. I watched speechlessly as she opened them. There was no way our parents were letting her spend that much money- online or off!

     "How much did all of this coat?"

     "Oh, only about $15 in all!" She said excitedly. "Everything on eBay is on sale! It's way better than

going to the mall."

     I felt as if there had been a store right in my backyard that I had never walked into! That week, I ordered a used Spanish textbook for my summer course online for 10 percent of the publishing price. A few

days later, I bought an iPod protector and a book or two via the wonderful eBay.com.

1. From the first two paragraph we can conclude that the author          .

A. had noexperience using computers

B. had no idea of what e-commerce is

C. only used the Internet to check e-mail

D. thought surfing the Internet was a waste of time

2. The writer didn't find out about e-commerce until          .

A. he stopped web-surfing

B. he visited a store in his backyard

C. his friends told him about the online deals they made

D. his sister explained the packages she got by mail

3. We can infer from the last paragraph that the author           .

A. has begun to enjoy online shopping

B. loves the big store in her backyard

C. feels she is a true master of the Internet

D. never enjoyed shopping that much

4. What's the purpose of the article?

A. To make an online shopping ad.

B. To do business on the Internet.

C. To tell the readers how he begins online shopping.

D. To advise people not to do online shopping

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