在一定条件下，将3 mol A和1 mol B两种气体混合于固定容积为2 L的密闭容器中，发生如下反应：3A(g)＋B(g)
xC(g)＋2D(g)。2 min末该反应达到平衡，生成0.8 mol D，并测得C的浓度为0.2 mol·L－1。下列判断正确的是
A．A的转化率为40%
B．2 min内B的反应速率为0.2 mol·(L·min)－1
C．x＝2
D．若混合气体的密度不变，则表明该反应已达到平衡状态
答案：A
生成0.8 mol D，则消耗A是1.2mol，所以A的转化率是1.2÷3×100％＝40＆，A正确。消耗B是0.4mol，所以B物质反应速率是0.4mol÷2L÷2min＝0.1mol·(L·min)－1，B不正确。C的浓度为0.2 mol·L－1，则生成C是0.2 mol·L－1×2L＝0.4mol，所以根据变化量之比是相应的化学计量数之比可知，x＝1，C不正确。密度是混合气的质量和容器容积的比值，在反应过程中质量和容积始终是不变的，D不正确。答案选A。
第II卷 书面表达(共两题，满分15分) 1. 阅读填空题 阅读下面短文，并根据短文内容完成填空题（共5个小题，每小题1分，满分5分）。 A recent study shows that nearly 50 percent of the school kids in Beijing do not have breakfast. They tend to feel sleepy all day and have bad memories, so it is hard for them to get high marks in all kinds of tests. Some students who study deep into the night choose to miss breakfast so that they can have a few extra minutes in bed. Others are given money to buy their breakfast on the way to school because their parents are too busy to prepare it for them. In addition, a few school girls want to stay slim and often go to school without breakfast.. In fact, the morning meal plays an important part. It can provide 30 percent of the whole day’s energy. For a creative mind and better judgment, school kids should start their days with a regular breakfast. Statistics（统计）about school kids’ not having breakfast
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