142.
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
答案选(D)
能请各位大大解释一下题意及解法吗??实在不能理解,谢谢
题目的大概意思是:一个化学反应的速度与物质A的浓度的平方成正比,与物质B的浓度成反比. 现在如果B的物质浓度提高100%(即变成2倍),要使保持此化学反应的速度不变, 那么A物质的浓度应该如何变化.
我是这样思考的:
1)反应的速度与B 的浓度成正比, 当B浓度变成2倍时,若A的浓度不变的时候,反应速度本应变成原来的2倍.
2)按照题目的意思反应速度要不变,必定要让A的浓度的平方也增加2倍.所以A的浓度应该变成原来的(根号2)倍,即A的浓度增加约40%
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