问题 选择题

哈珀因分明了由氮气和氢气合成氨气的方法而获得1918年诺贝尔化学奖.现向一个容积为2L的恒容的密闭容器中,加入N2、H2各4mol,在一定条件下使合成氨气反应发生,反应在10s时达到了反应的限度,这是H2的平均反应速率为0.12mol/(L•s),下列一个说法正确的是(  )

A.容器中混合气体的密度增大

B.此时容器中气体的压强是反应前气体压强的0.8倍

C.达到反应限度时H2的转化率是20%

D.此时容器中N2的物质的量为1.6mol

答案

A、N2(g)+3H2(g)

2NH3(g),反应前后都是气体,根据质量守恒,可知反应前气体的总质量和达到反应的限度时气体的总质量相等,容器的体积不变,所以密度不变,故A错误;

B、H2的平均反应速率为0.12mol/(L•s),则反应的H2的物质的量浓度为0.12mol/(L•s)×10s=1.2mol/L,反应的H2的物质的量为1.2mol/L×2L=2.4mol,根据化学平衡三段法可知:

                N2(g)+3H2(g)

2NH3(g)

起始(mol)      4       4                 0

反应(mol)     0.8     2.4               1.6

10s(mol)      3.2     1.6               1.6

反应前气体总的物质的量为:8mol,10s时气体总的物质的量为6.4mol,所以10s容器中气体的压强是反应前气体压强的0.8倍,故B正确;

C、由选项B可知反应的氢气为2.4 mol,则氢气的转化率为:

2.4 
  4 
×100%=60%,故C错误;

D、由选项B可知容器中N2的物质的量为3.2mol,故D错误;

故选B.

判断题
单项选择题

(二)

Some spiders hunt on the ground, others build webs to trap their food, but the grass water spider catches its prey by running along the surface of the water.

This special water spider lives on the grassy banks of streams where mosquitoes, damsel flies and other insects come to feed and breed.

Although it is one of the largest spiders in New Zealand, it has an unusual ability. It doesn’t disturb the water as it waits for its meal, and there~ is barely a ripple when it skims across the surface at lightning speed to catch its prey.

Grass water spiders deal swiftly with larger insects like damsel flies by pulling their heads under the water and holding them there until they drown.

After a meal, the grass water spider spends up to half an hour grooming itself. It wipes its eight eyes, brushes its antennae, and takes special care to clean the hairs on its body.

It is the hairs that trap tiny bubbles of air so that the spider can run down a blade of grass and stay underwater for up to an hour when it is frightened. The hairs also keep the spider dry, even underwater.

It is only when the female spider is caring for the young that she does not hunt on the water. After mating, she produces a large egg sac, which she carries around for five weeks. Once the eggs start to hatch, she attaches the sac to some blades of grass or a thistle. She then tears the sac open and releases the tiny spiders into the nursery web.

The passage tells us that the spider ().

A.feeds grass and thistles to its young

B.lives on blades of grass under the water

C.lives in the grass on the banks of streams

D.eats a meal once every five weeks