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The rate of a certain chemical reaction is directly

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The rate of a certain chemical reaction is directly [#permalink] New post 17 Dec 2006, 00:02
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 chemicl B present. If the concentration of chemical B is increased by 100% which of the following is the closest to the percentage change in the concentration of chemical A required to keep the reacton rate unchanged?

100% decrease
50% decrease
40% decrease
40% increase
50% increase

OA: D
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 [#permalink] New post 17 Dec 2006, 01:00
Say A is the concentration of Chemical A and B is concentration of Chemical B
Then Rate = k * A^2 / B
B is increased by 100%, means the new conc is 2B
Rate = x^2 / 2B = A^2/B
=> new concentration of A = sqrt2 A
% = [(sqrt2*A –A)/A] * 100 = 41% increase
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 [#permalink] New post 17 Dec 2006, 01:59
anindyat wrote:
Say A is the concentration of Chemical A and B is concentration of Chemical B
Then Rate = k * A^2 / B
B is increased by 100%, means the new conc is 2B
Rate = x^2 / 2B = A^2/B
=> new concentration of A = sqrt2 A
% = [(sqrt2*A –A)/A] * 100 = 41% increase

A2..
Same approach as anindyat but used numbers instead.
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 [#permalink] New post 17 Dec 2006, 09:01
I understand. Thank you.
  [#permalink] 17 Dec 2006, 09:01
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