问题 选择题

在一定温度的定容密闭容器中,反应A2(g)+B2(g)

2AB(g)达到平衡状态的是(  )

A.混合气体的密度不再改变

B.容器内的总压强不随时间而变化

C.单位时间内生成2nmolAB的同时,生成nmol的B2

D.A2、B2、AB的分子数之比为1:1:2时

答案

A、根据质量守恒,化学反应前后混合物的质量不变,容器体积不变,所以密度始终不变,故A错误;

B、该反应前后气体体积不变,所以压强始终不变,故B错误;

C、位时间内生成2nmolAB的同时,生成nmol的B2,说明正逆反应速率相等,所以达到平衡状态,故C正确;

D、反应达到平衡时的浓度与反应的初始物质的量以及反应的转化程度有关,所以不能确定是否达到平衡,故D错误;

故选C.

完形填空
完形填空。
    Stone is all around us. Stone is usually very hard,  1  it can also be soft. Stones
have many uses.
    In some  2 , artists carve (雕刻) beautiful things out of soft stones, because they
can be shaped easily. In ancient times, people carved  3  persons or animals out of soft
stones, which could be carried along with. While in some European countries, statues (雕塑)
are carved  4  hard stones and they do not change easily. In summer, the hot sun  5  on
these statues and in winter the snow falls on them, but they  6  remain beautiful.
    Stone is strong and long-lasting. So, it is  7  enough for building. A house built of
stone does not catch fire as easily as  8  made of wood. Some stones are coloured, so they
make the  9  look wonderful. People can also get a fire with stones. Besides, some kinds
of stones can be used to  10  jewellery (珠宝). We've found stones are really amazing.
( )1. A. and      
( )2. A. countries    
( )3. A. young     
( )4. A. into      
( )5. A. shines    
( )6. A. even      
( )7. A. good      
( )8. A. this      
( )9. A. stones    
( )10. A. find      
B. but      
B. cities  
B. old      
B. of      
B. drops    
B. still    
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B. none    
B. buildings      
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C. factories      
C. small    
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C. fire    
C. buy      
D. so     
D. parks  
D. big    
D. from   
D. fits   
D. often                   
D. old    
D. it     
D. wood   
D. make   
单项选择题