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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: xc630 on January 22, 2008, 10:45:48 PM

Title: catalysts & rxn rates
Post by: xc630 on January 22, 2008, 10:45:48 PM

Hello,

I would appreciate if anyone could explain the following problem:

The activation energy of an uncatalyzed reaction is 95 kj/mol.  The addition of a catalyst lowers the Ea to 55 kj/mol.  Assuming the collision factor remains the same, by what factor will the catalyst increase the rate of the reaction at (a) 25 degrees celsius and b) 125 degrees celsius.

The answer is a) the catalyzed rxn is 10,000,000 times faster at 25 degrees C and b)  the catalyzed rxn is 180,000 times faster at 125 degrees C.

I tried using the Arrhenius equation to compare but did not get anything close to the answers.

Title: Re: catalysts & rxn rates
Post by: enahs on January 22, 2008, 11:31:08 PM

Can you show how you are doing it? As when I solve it using the Arrhenius equation I get the same general answers.

Make sure you are converting kJ to J.

Title: Re: catalysts & rxn rates
Post by: xc630 on January 23, 2008, 01:43:44 PM

I guess I'm confused on what I'm supposed to plug in and compare.

The Arrhenius equation is k= Ae^(-Ea/RT) 

I'm supposed to compare the rates but isn't k the rate constant?  Also, if I am to use this formula what would be the temperature for the uncatalyzed reaction? 

Title: Re: catalysts & rxn rates
Post by: xc630 on January 23, 2008, 05:24:56 PM

Never mind I got it. thanks