PS #142

foreversun99

142.    14580-!-item-!-187;#058&010013
The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present.  If the concentration of chemical B is increased by 100 percent, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

(A) 100% decrease
(B) 50% decrease
(C) 40% decrease
(D) 40% increase
(E) 50% increase
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【答案】D
題目意思是說 化學物A的平方與此化學反應速率成正比
化學物B 與此化學反應速率成反比
但不懂要如何從B推得A?

wenjie87

题目中要求是要保持不变的嘛

foreversun99

SORRY~能否有那位能解釋的詳細一點?

wenjie87

SORRY~能否有那位能解釋的詳細一點?

-- by 会员 foreversun99 (2010/8/30 22:58:16)

我真想去睡美容觉了……
设The rate of a certain chemical reaction 为X
则X=A^2/B
B增加100%，要使得X不变，A应该怎么变化？设A的变化为y
则，X=[A(1+Y)]^2/2B    =>    (1+y)^2=2    =>      y=根号2-1， 所以y约等于0.4