Problem Solving - 35

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

Answer: D

rate = k*(A1^2)/B
If concentration of chemical B is increased by 100 percent then
rate = k*(A2^2)/2B

(A2/A1) ^ 2 = 2
A2/A1 = Square root (2)
(A2/A1) - 1 = Square root (2)-1 = 0.414
(A2-A1)/A1 = 0.414 = 40% approximately