[問題]新PP-test1的一道題

[jim9619]

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 B present. If the concentration of chemical B is increased by 100 precent, which of the following is closrt to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

A.100% decrease
B. 50% drease
C. 40% drease
D. 40% increase
E. 50% increase

答案是D...
不是很懂題目在問什麼??
麻煩高手詳解一下
感激不盡阿~~

[zazer.lin]

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 B present. If the concentration of chemical B is increased by 100 precent, which of the following is closrt to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

A.100% decrease
B. 50% drease
C. 40% drease
D. 40% increase
E. 50% increase

答案是D...
不是很懂題目在問什麼??
麻煩高手詳解一下
感激不盡阿~~

題目的大意是說:
一個化學反應率和A溶液體積的平方成正比,和B溶液體積成反比.
題目問說,當B溶液體積增加100%時,A物質需要增加(or減少)多少體積,才能使其化學反應率不變.

反應率 = A[sup]2[/sup] / B ........<I>
由於題目所需反應率不變, 所以反應率為1, 故<I>可改寫成
<I> ==> 1 = A[sup]2[/sup] / B
==> A[sup]2[/sup] = B........<II>

當B增加100%後(newB = B + 100%B = 2B),整個化學反應率需不變, 所以
1 = newA[sup]2[/sup] / newB
==> 1 = newA[sup]2[/sup] / 2B
==> newA = (2B)[sup]1/2[/sup]
==> newA = (2A[sup]2[/sup])[sup]1/2[/sup] .........by <II>
==> newA = 1.41A

所以A需要約略增加40%