问题 问答题

市售打火机里装的不是汽油,而是液体丁烷(C4H10).丁烷在空气中完全燃烧后产生二氧化碳和水蒸气.写出丁烷完全燃烧的化学方程式______.

答案

丁烷与氧气在点燃条件下完全反应生成二氧化碳和水蒸气.

该反应的化学方程式为:2C4H10+13O2

 点燃 
.
 
8CO2+10H2O.

故答案为:2C4H10+13O2

 点燃 
.
 
8CO2+10H2O.

单项选择题

In 1998 consumers could purchase virtually anything over the Internet. Books, compact discs, and even stocks were (1) from World Wide Websites that seemed to (2) almost daily a few years earlier, some people had predicted that consuners accustomed to shopping in stores would be (3) to buy things that they could not see or touch (4) . For a growing number of time-starved consumers, however, shopping from their home computer was proving to be a convenient (5) to driving to the store.

A research estimated that in 1998 US consumers could purchase $ 7.3 billion of goods over the Internet, double the 1997 total. Finding a bargain was getting easier, (6) the rise of online auctions and Websites that did comparison shopping on the Internet for the best (7) .

For all the consumer interest, (8) in eyberspaee was still a largely (9) business, however. Internet pioneer Amazon. eom, which began selling books in 1995 and later (10) into recorded music and videos, posted (11) of $ 153.7 million in the third quarter, up from $ 37.9 million in the same period of 1997. Overall, (12) , the company’ s loss widened to $ 45.2 million from $9.6 million, and analysts did not expect the company to turn a profit (13) 2001. (14) the great loss, Amazon. tom had a stock market value of many billions, reflecting investors’ (15) about the future of the industry.

Internet retailing appealed (16) investors because it provided an efficient means for reaching millions of consumers without having the cost of operating (17) stores with their armies of salespeople. Selling online carried its own risks, however, (18) so many companies competing tor consumers’ attention, price competition was (19) and profit (20) thin or nonexistent.

13()

A.in

B.by

C.after

D.until

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