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concentration

by adam15 » Mon Nov 23, 2009 1:02 pm
43) The rate of a reaction is directly proportional to the square of the concentration of A and inversely proportional to concentration of B. If B increases by 100%, which of the following is closest to the % change in concentration of A required to keep the rate unchanged?
a. 100% decrease
b. 50% decrease
c. 40% decrease
d. 40% increase
e. 50% increase
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by mp2437 » Mon Nov 23, 2009 1:59 pm
rate is proportional to square of A and inversely proportional to B, so rate = A^2 / B. Say A = B = 1, so rate = 1. Now you are told that B increases by 100%, so B = 2. How much do you have to increase/decrease A to keep rate = 1?


rate = 1 = A^2 / B --> 1 = A^2 /2 --> A^2 = 2 --> A = sqrt(2) ~ 1.41. So A went from 1 to 1.41, or an increase of 40%. Choice D.
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by adam15 » Mon Nov 23, 2009 2:49 pm
thanks for the solution, it appears easier than I thought.
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