题目

可逆反应aA(g)＋bB(g)cC(g)的正、逆反应速率可用各反应物或生成物浓度的变化来表示。下列各关系式中能说明反应已达到平衡状态的是( ) A．av正(A)＝bv正(B)                         B．bv正(A)＝av逆(B) C．av正(C)＝cv正(A)                         D．av正(A)＝bv逆(B) 答案：．B [化学平衡建立时，v正＝v逆，对于不同物质而言，要符合物质的反应速率之比等于化学计量数之比的要求。同时必须要使反应方向不同，A、C选项方向都是正反应；B选项方向相反且符合v正(A)∶v逆(B)＝a∶b，符合题意，D选项错误。] 听下面一段材料,回答第1-3题.1．What prevents the man taking the Shakespeare course?A．It's already full.B．It's very expensive.C．It requires a starter course.2．What problem does the man have?A．He can't take evening classes.B．His boss won't give him a leave.C．He has to take the course many times.3．What will the man do?A．Give up his job at the caf ?.B．Check the course at another college.C．Change his work hours with his friend.