问题 问答题

在2L和密闭容器中放入4molN2O5,发生如下反应:2N2O5(g)═4NO2(g)+O2(g)反应进行到5min时,测得N2O5转化了20%,求:

(1)5min时,剩余N2O5的物质的量;

(2)前5min,v(NO2)为多少;

(3)5min时,N2O5的物质的量占混合气体总物质的量的百分比.

答案

(1)转化的N2O5的物质的量=4mol×20%=0.8mol,故剩余N2O5的物质的量=4mol-0.8mol=3.2mol,

答:5min时,剩余N2O5的物质的量为3.2mol.

(2)根据三段式解题法,求出反应混合物各组分物质的量的变化量、5min时各组分的物质的量,

2N2O5(g)4NO2(g)+O2(g)

开始(mol):40 0

变化(mol):0.8 1.6 0.4

5min时(mol):3.21.6 0.4

所以υ(NO2)=

1.6mol
2L
5min
=0.16mol/(L•min);

答:υ(NO2)为0.16mol/(L•min).

(3)5min时,N2O5占混合气体总体积的百分比为

3.2mol
3.2mol+1.6mol+0.4mol
×100%=61.5%,

答:5min时,N2O5占混合气体总体积的百分比为61.5%.

单项选择题
阅读理解

阅读理解。

      Do you love holidays but hate the increase weight that follows? You are not alone.

      Holidays are happy days with pleasure and delicious foods. Many people, however, are worried about the

weight that comes along with these delicious foods.

      With proper planning, though, it is possible to control your weight. The idea is to enjoy the holidays but

not to eat too much. You don't have to turn away from the foods that you enjoy. The following suggestions

may be of some help to you.

      Do not miss meals. Before yon leave home for a feast (宴会), have a small, low-fat snack (小吃). This

may help to keep you from getting too excited before delicious foods. Begin with clear soup and fruit or

vegetables. A large glass of water before you eat may help you feel full. Use a small plate; a large plate will

encourage you to have more than enough. 

      Better not have high-fat foods. Dishes that look oily or creamy have much fat in them.

      Choose lean meat (瘦肉). Fill your plate with salad and green vegetables.

      If you have a sweet tooth, try mints (薄荷) and fruits. They don't have fat content as cream and

chocolate.

      Don't let exercise take a break during the holidays. A 20-minute walk after a meal can help burn off

excess (过多的) calories (卡路里).

1. Holidays are happy days with pleasure but they may _____. [ ]

A. bring you much trouble in your life

B. bring weight problems

C. make you worried about your foods

D. make you hate delicious foods

2. In order to really enjoy your holidays without putting on weight, you'd better _____. [ ]

A. not eat the food in high fat

B. drink much water and have vegetables only

C. not accept invitations to feasts

D. turn away from delicious foods

3. According to the passage, _____ is a necessary part to stop you from putting on weight.[ ]

A. vegetables

B. water

C. calories of energy

D. physical exercise

4. Excess calories can be found in your body in the form of _____. [ ]

A. energy

B. fat

C. food

D. something invisible (看不见)