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# The rate if a certain chemical reaction is directly

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Current Student
Joined: 27 Jul 2007
Posts: 872
Location: Sunny So Cal
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The rate if a certain chemical reaction is directly [#permalink]

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22 Jul 2008, 09:30
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

The rate if a certain chemical reaction is directly proportional to the square of the concentration of chemical A 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 percentage 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
Senior Manager
Joined: 06 Apr 2008
Posts: 401

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22 Jul 2008, 09:36
ryguy904 wrote:
The rate if a certain chemical reaction is directly proportional to the square of the concentration of chemical A 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 percentage 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

Conc of A should increase by sqrt 2 times = 1.414 = 40% increase

Current Student
Joined: 27 Jul 2007
Posts: 872
Location: Sunny So Cal
Schools: CBS, Cornell, Duke, Ross, Darden

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23 Jul 2008, 09:56
bump.

Thanks!
Manager
Joined: 20 May 2008
Posts: 55

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24 Jul 2008, 16:34
Ca = Concentration of A
Cb = concentration of B

Rate = k (Ca^2 / Cb)

Now Cb is increased by 100 %

Cb = Cb + (100/100)Cb
= 2Cb

Now to balance the equation

Let x = new Ca to balance the concentration

Ca^2 / Cb = x^2 / 2*Cb

x^2 = 2 * Ca^2
x = sqrt 2 * Ca
= 1.414 * Ca
= 40 % Ca (increase)
Senior Manager
Joined: 19 Mar 2008
Posts: 350

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24 Jul 2008, 23:23
1
KUDOS
R= rate of chemical reaction
A = Concentration of chemical A
B = Concentration of chemical B
k = constant

R = k * A^2 / B

k * A^2 / B = k * a^2 / 2B
(a/A)^2 = 2
a/A = 2^0.5 = 1.4

d
Retired Moderator
Joined: 18 Jul 2008
Posts: 921

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25 Jul 2008, 13:21
You are using "a" and "A". What is the difference?

I also don't understand how you are solving here:

k * A^2 / B = k * a^2 / 2B
(a/A)^2 = 2
a/A = 2^0.5 = 1.4

Can you explain? I'm a lil lost. Thanks.

judokan wrote:
R= rate of chemical reaction
A = Concentration of chemical A
B = Concentration of chemical B
k = constant

R = k * A^2 / B

k * A^2 / B = k * a^2 / 2B
(a/A)^2 = 2
a/A = 2^0.5 = 1.4

d
Re: Chemical Reaction   [#permalink] 25 Jul 2008, 13:21
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# The rate if a certain chemical reaction is directly

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