请教一道math题谢谢

superdanouc · 发表于 2011-3-7 17:18:00

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%,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
ans:B
why? 怎么列式子？谢谢

molynca0717 · 发表于 2011-3-7 17:34:26

嘿嘿~我又出现了~~

你这B选项没错么。。

superdanouc · 发表于 2011-3-7 17:45:25

嘿嘿~我又出现了~~

你这B选项没错么。。

-- by 会员 molynca0717 (2011/3/7 17:34:26)

对呀
我想了半天也不知为什么？谢谢喔

superdanouc · 发表于 2011-3-7 18:44:41

求解帮帮忙

molynca0717 · 发表于 2011-3-7 19:15:30

我帮忙翻译下题干吧。说某化学反应的速率，与A试剂浓度的平方成正比，并与B试剂浓度成反比。
现在如果B试剂的浓度提高100%---也就是2倍，以下哪项能够使反应速率不变？

总之根据我高中学化学的知识。。应该A的浓度要增加的，增加41.4%。。

sdcar2010 · 发表于 2011-3-7 19:26:30

1、The rate of a certain chemical reaction is directly proportaional 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%, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

Rate = [A]*[A]/[B]

So [A]*[A]/[B] = [x*A]*[x*A]/[2B]

x*x = 2

x = 1.414

So A increases around 40% . LS is right.

superdanouc · 发表于 2011-3-7 20:22:40

我帮忙翻译下题干吧。说某化学反应的速率，与A试剂浓度的平方成正比，并与B试剂浓度成反比。
现在如果B试剂的浓度提高100%---也就是2倍，以下哪项能够使反应速率不变？

总之根据我高中学化学的知识。。应该A的浓度要增加的，增加41.4%。。

-- by 会员 molynca0717 (2011/3/7 19:15:30)

谢谢喔
我明白了
九号要给力呀

superdanouc · 发表于 2011-3-7 20:23:30

1、The rate of a certain chemical reaction is directly proportaional 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%, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

Rate = [A]*[A]/

So [A]*[A]/ = [x*A]*[x*A]/[2B]

x*x = 2

x = 1.414

So A increases around 40% . LS is right.
-- by 会员 sdcar2010 (2011/3/7 19:26:30)

你的解释给我的启示很大
原来公式化这个题目呀
十分谢谢！！

Zhongtianwu · 发表于 2011-3-8 23:32:01

非常感谢superdanouc, 清晰明了。

kkmzhou · 发表于 2011-3-9 19:18:37

不好意思，可以解释一下“ 现在如果B试剂的浓度提高100%---也就是2倍” 是这么知道的呢？
谢谢哦

请教一道math题谢谢

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