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by Deepthi Subbu » Sun Dec 12, 2010 2:50 am
The rate of a certain chemical reaction is directly proportional to the square of concentration of Chemical A and inversely proportional to the concentration in chemical B . If the concentration of chemical B is increased by 100 percent , which of the following is closest to the percentage change in concentration of chemical A required to keep the chemical reaction unchanged?

1. 100 % decrease
2.50 % decrease
3.40% decrease
4.40 % increase
5. 50 % increase

OA D
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by limestone » Sun Dec 12, 2010 3:56 am
The concentration of chemical B is increased by 100%, or concentration of chemical B has doubled.

Concentration of chemical B (call it CB) is inversely proportional to the rate of chemical reaction (R). As CB is doubled, R is slowed down twice.

To keep the rate of chemical reaction (R) unchanged, we must use concentration of chemical A (CA) to speed R up twice.

As given, R is directly proportional to square of CA. To speed R up twice, we must have square of CA doubled.

Square of CA = 2 then
CA = sqrt (2) = 1.4142
Thus CA must be increased by 41.42%
Pick D.
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