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### Topic: rate constant calculation  (Read 4762 times)

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#### Mel22

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##### rate constant calculation
« on: March 30, 2006, 12:46:41 PM »
Hello everyone!

I have some trouble finding the correct solution for the following problem:

The eliminaion of carbon dioxide from pyruvate ions by a decarboxylase enzyme was monitored by measuring the partial pressure of the gas as it was formed in a 250 mLflask at 20°C. In one experiment the partial pressure increased from zer o to 100 Pa in 522 s in a first order reaction when the initial concentration of pyruvate ions in 100 mL of solution was 3.32 mmol / L. What is the rate constant of the reaction?____________________________________________________________________________________________________

This is what I attempted:

strategy: use the 1st order integrated rate law (with partial pressures) and consider the consumption of pyruvate ions.

integrated first order rate law:

ln(p-final) = ln(p-initial) - kt

p initial

p = nRT / V = 0.0315 bar

where V = 0.25l

and n = c*V = 3.23 mmol/l *0.1 l = 3.23*10^(-4)

p final

p final = p-initial - delta p = 0.0315 bar - 0.001 bar = 0.0305 bar

rate constant k

k' = -k = -6.2 * 10^(-5) 1/s
->
k = 6.2 *10^(-5) 1/s
the correct answer, however, is 4.2* 10^(-5) 1/s

Does anyone see what I am doing wrong?
Thanks so much for any help/hints/suggestions!
« Last Edit: March 30, 2006, 12:52:31 PM by Mel22 »