一道ps,完全没思路，童鞋们看看啊

chanxu

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


题目啥意思啊 看了半天也不明白 跪求牛牛解答。

tracytrace

恩,我是这么看哦
这个咚咚(反应)和A咚咚的平方有关,和B反比. reaction=aA^2*(1/b) B
那么现在B变成了2倍,再考虑个倒数,A平方就要发生两倍的关系,开根号就是1.414喽.所以Increase 40%

naturalwater

directly proportional to the square of the concentration of chemical A
跟A^2成正比
inversely proportional to the concentration of chemical B present
跟B成反比
就是说Rate＝k(A^2)/B
现在B变成B(1+100%)问A要如何变化才能使Rate不变
设A变化x%
kA^2/B=k[A(1+x%)]^2/B(1+100%)
所以x%=41.4%

hzd515976083

化学反应速率r与A的浓度的平方成正比，与B的浓度成反比。当B的浓度增加1倍时，问A浓度如何变化以保证r不变

思路：B变成原来的2倍，A平方也要变成原来的两倍，所以百分比变化就是2^(1/2)-1=0.414

chanxu

谢谢楼上们的答复。