问题 选择题

下列能表明可逆反应:A+2B

2C 已达平衡状态的是(  )

A.A、B、C的浓度相等

B.当生成1molA的同时也生2molB

C.A、B、C的物质的量比为1:2:2

D.当生成1molA的同时也生成2molC

答案

A.A、B、C的浓度相等,仅能代表化学平衡状态的特殊个例,对判断一个可逆反应是否建立化学平衡没有普遍意义,故A错误;

B.生成A和生成B都代表逆反应速率.生成1molA,同时生成2amolB,只是说明了逆反应按照计量数生成A和B而已,不能说明正反应速率与逆反应速率相等,故B错误;

C.A、B、C物质的量之比等于1:2:2,只能说明A、B、C的物质的量之比等于化学计量数之比,仅能代表化学平衡状态的某种特殊情况,对判断一个可逆反应是否建立化学平衡没有普遍意义,故C错误;

D.生成A代表逆反应速率,生成C代表正反应速率,生成1molA的同时也生成2molC,说明用A表示的逆反应速率与用C表示的正反应速率之比等于化学方程式中对应的计量数之比,即正反应速率等于逆反应速率,故D正确;

故选D.

阅读理解

What do people do with their old, out of date but still useful computers? Most people don’t know how to deal with them. Many old computers are put away. Many more are simply thrown away as rubbish.

Finally, some companies are thinking of ways to bring down the number of old computers. Sony has agreed to help recycle old Sony products(产品). Dell, Hewlett Packard and other companies now also take back some old computers of their own brands.

In some countries, laws have been passed, too. Computer companies have to pay for collecting and recycling their used products. And 70% of computer waste must be recycled. The idea behind the laws is that computer companies themselves should pay for the cost. That will encourage them to make computers which are easier and cheaper to repair and upgrade(升级).

Yet many people are throwing away good computers, while others cannot afford them at all. Hundreds of organizations are working on this problem. They collect and repair old computers. Some also teach others how to repair computers. These repaired computers then go to schools, charities(慈善团体) or people who need them. Giving a used computer to one of these organizations can turn one person’s rubbish into someone else’s useful things and cut down waste, too.

根据短文内容,选择正确答案。(10分)

小题1:What do many people do with old computers?

A.They sell them.  B.They send them to others.    C.They stop using them.

小题2:How many computer companies are mentioned in the second paragraph?

A.One.             B.Two.                 C.Three.

小题3:According to the laws in some countries, computer companies must       .

A.recycle most of their products

B.collect all their used products

C.make more cheaper computers

小题4:What do the organizations do to solve the problem of old computers?

A.Help the computer companies to collect them.

B.Repair and send them to those who need them.

C.Help people to learn to use them.

小题5:What is the main idea of this passage?

A.Repairing old computers.

B.Encouraging to make cheap computers.

C.Recycling old computers.        

单项选择题