问题 选择题

一定温度下,在固定容积的密闭容器中,可逆反应mA(g)+nB(g)⇌pC(g)+qD(g),当m、n、p、q为任意正整数时,下列状态一定能说明反应已达到平衡的是(  )

①体系的压强不再发生变化②体系的密度不再发生变化

③各组分的物质的量浓度不再改变 ④各组分的质量分数不再改变

⑤反应速率VA:VB:VC:VD=m:n:p:q.

A.只有③④

B.②③④

C.①②③④

D.①②③④⑤

答案

①如果该反应是一个反应前后气体体积不变的可逆反应,则体系的压强始终不变,所以不能根据压强判断反应是否达到平衡状态,故错误;

②反应前后混合气体的质量不变,容器的体积不变,所以体系的密度始终不变,所以不能据此判断该反应是否达到平衡状态,故错误;

③各组分的物质的量浓度不再改变,该反应达到平衡状态,故正确;

④反应到达平衡状态时各组分的物质的量不再改变,各组分的质量分数不再改变,故正确;

⑤反应速率之比等于计量数之比反应后任何时刻都正确,属于当反应速率vA:vB:vC:vD=m:n:p:q,不能据此判断该反应是否达到平衡状态,故错误;

所以只有③④正确;

故选:A.

单项选择题
单项选择题

To be a good friend, you have to give of yourself, nonetheless not so much that you lose yourself. This is a pretty predictable recipe for happiness. Giving to others—a reliable way of fostering friendships—makes us happier than taking things for ourselves. In the light of research led by Dr. Elizabeth Dunn at the University of British Columbia, money can purchase happiness...on the prerequisite that you utilize it on other people.

Researchers administered three studies consecutively. First, they surveyed more than 600 Americans and found that spending money on gifts and charities led to greater happiness than spending money on oneself.

Subsequently they probed into workers who had just received bonuses and observed that their happiness did not hinge on the size of their bonus but on the decision they made about what to do with whatever amount of money they received. Those who spent more of their bonus on others were happier than those who spent the money on themselves.

Finally, the researchers simply distributed money to a good many subjects, instructing some to spend the money on themselves and others to spend the money on others. At the end of the day, the ones who spent money on others were a good deal happier.

As a consequence, having friends and treating them generously is clearly a winning strategy in life. But what about in business

If you watch even a single episode of any reality TV show based on a competition, such as The Apprentice, you’ll hear a single phrase crop up more often than any other: "I’m not here to make friends!" Is that true Are we better off being cutthroat than collaborative

Once you’re on the job, having a best friend at work is a p predictor of ensuing success. People might define "best" loosely (think of this as kindergarten where you can have more than one "best" friend), but according to a Gallup Organization study of more than 5 million workers over 35, 56% of the people who say they have a best friend at work are engaged, productive, and successful while only 8% of the ones who don’t are.

Another remarkable study, spanning decades, revealed that friendships in high school were an effective predictor of increased wages in adulthood—to the tune of 2% per person who considered you a close friend. To put it otherwise, if in high school three people regarded you as one of their closest same-sex friends, your earnings in adulthood work would be 6% higher.

The happy truth is that the competitors who say they’re not here to make friends don’t win eventually. That’s true for reality TV, for business, and for life as well.

According to Dr. Elizabeth Dunn’s research, ()

A. you’ll gain friendship if you are ready to sacrifice

B. giving of yourself can secure you much happiness

C. money can make you happy if employed in a proper way

D. accepting things from others may not make us happy