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posted by  ss83 on 7/7/2008 9:30:05 PM  |  status: Live  

if correct will give lifesaver! thank you

Course Textbook Chapter Problem
General Chemistry N/A 14 N/A
Question Details:

Learning Goal: To understand the relationship between the equilibrium constant and rate constants.

For a general chemical equation

\rm A+B \rightleftharpoons C+D

the equilibrium constant can be expressed as a ratio of the concentrations:

K_{\rm c}={\rm \frac{[C][D]}{[A][B]}}

If this is an elementary chemical reaction, then there is a single forward rate and a single reverse rate for this reaction, which can be written as follows:

\matrix {\hfill \mbox{forward rate}&=&k_{\rm f}{\rm [A][B]}\hfill \cr \hfill \mbox{reverse rate}&=&k_{\rm r}{\rm [C][D]}\hfill \cr}

where k_f and k_r are the forward and reverse rate constants, respectively. When equilibrium is reached, the forward and reverse rates are equal:

k_{\rm f} {\rm[A][B]}=k_{\rm r} {\rm [C][D]}

Thus, the rate constants are related to the equilibrium constant in the following manner:

K_{\rm c}=\frac{k_{\rm f}}{k_{\rm r}}={\rm \frac{[C][D]}{[A][B]}}




For a different reaction, K_{\rm c}=3.42×10^{3}, k_{\rm f}=5.13×10^{3} <units>s^{-1}</units>, and k_{\rm r}=1.50 <units>s^{-1}</units>. Adding a catalyst increases the forward rate constant to 8.31×105 s^{-1}. What is the new value of the reverse reaction constant, k_r, after adding catalyst?
Express your answer numerically in inverse seconds.
  k_r  =
  \rm s^{-1}
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posted by AJ <3 on 7/7/2008 10:18:54 PM  |  status: Live
Asker's Rating: Helpful   
ss83's comment:
"I still need further assistance, I'm still not sure this is the correct answer. Thanks for your help!"
Response Details:
Test Send 

By this relationship:

Kc = kf / kr

So from the given information:

K_{\rm c}=3.42×10^{3} 
k_{\rm f}=5.13×10^{3} <units />s^{-1}</units> 
k_{\rm r}=1.50 <units />s^{-1}</units>.

Under the condition of a catalyst increasing the forward rate constant, we have:
K_{\rm c}=3.42×10^{3}          <--- The equilibrium constant is not affected by the catalyst.
 kf  = 8.31×105 s     <--- The rate constant is affected by the catalyst.
 kr  = ?                        <--- This is the unknown rate constant we are trying to find.

So using the equation from the beginning, Kc = kf / kr, plug everything in and solve for kr:

Kc = kf / kr
(kr) (Kc) = kf
kr = kf / Kc
    = 8.31×105 s / 3.42×103
    = 2.4 x 10-8 s

Please ask for further assistance.
Please ask for further assistance. AJ
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posted by AJ <3 on 7/8/2008 3:52:40 PM  |  status: Live
Asker's Rating: N/A   
Response Details:
Ok, which part do you need help on?
Please ask for further assistance. AJ
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