问题 填空题

下图中 

 表示氧原子,

表示氢原子:分别从物质组成,分子构成各说一观点

A、物质组成______

B、分子构成______

由此说明化学变化的实质______.

答案

A、由图中可知,分子由原子构成的,原子在化学变化前后没有改变,参加反应的各物质在反应前后元素的种类和原子的个数都不会发生改变;

A、从组成可得水中含有H、O两种元素等结论;

B、从构成上可知一个水分子由一个氧原子和两个氢原子构成等分子的结构,

由于原子是化学变化中的最小微粒,所以可知化学变化的实质是反应时分子分解为原子,原子再重新结合成新的分子,

故答案为:A、水是由氢和氧两种元素组成的;B、一个水分子是由1个氧原子和2个氢原子构成的.

化学变化中分子发生变化,分解成原子,原子重新组合成新分子.

阅读理解

     How often one hears children wishing they were grown-up, and old people wishing they were young

again. Each age has its pleasures and its pains, and the happiest person is the one who enjoys what each

age gives him without wasting his time in useless regrets.

     Childhood is a time when there are few responsibilities to make life difficult. If a child has good

parents, he is fed, looked after and loved, whatever he may do. It is impossible that he will ever again in

his life be given so much without having to do anything in return. In addition, life is always presenting new

things to the child—things that have lost their interest for older people because they are too well-known.

But a child has his pains: he is not so free to do what he wishes to do; he is continually being told to do

things, or being punished for what he has done wrong.

     When the young man starts to earn his own living, he can no longer expect others to pay for his food,

his clothes, and his room, but has to work if he wants to live comfortably. If he spends most of his time

playing about in the way that he used to as a child, he will go hungry. And if he breaks the laws of society

as he used to break the laws of his parents, he may go to prison. If, however, he works hard, keeps out

of trouble and has good health, he can have the great happiness of building up for himself his own position

in society.

1. According to Para. 2, the writer thinks that_____.

A. life for a child is comparatively easy

B. a child is always loved whatever he does

C. if much is given to a child, he must do something in return

D. only children are interested in life

2. After a child grows up, he______.

A. will have little time playing

B. has to be successful in finding a job

C. can still ask for help when in trouble

D. should be able to take care of himself

3. Which of the following statements is NOT true according to the passage?

A. People are often satisfied with their life

B. There are fewer interesting things for old people

C. Adults are freer to do what they want to

D. Adults should no longer rely on others

4. The main idea of the passage is_____.

A. life is not enjoyable since each age has some pains.

B. young men can have the greatest happiness if they work hard

C. childhood is the most enjoyable time in one's life

D. one is the happiest if he can make good use of each age in his life.

5. The paragraph following this passage will most probably discuss_____.

A. examples of successful young men

B. how to build up one's position in society

C. joys and pains of old people

D. what to do when one has problems in life

多项选择题