## 7E.3 in 7th edition

$\frac{d[R]}{dt}=-k[R]^{2}; \frac{1}{[R]}=kt + \frac{1}{[R]_{0}}; t_{\frac{1}{2}}=\frac{1}{k[R]_{0}}$

aisteles1G
Posts: 117
Joined: Fri Sep 28, 2018 12:15 am

### 7E.3 in 7th edition

the problem says "the presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 125 kj to 75 kj, by what factor does the rate increase at 298, all other factors equal?" I tried to do this using the Kr2/Kr1= e^-(Ea2-Ea1)/RT but keep ending up with the wrong answer than the solutions manual. The solutions manual for some reason does -(.4*125)/RT for the exponent instead of -(125-75kj)/RT and i cant understand why, thanks for any help!

armintaheri
Posts: 68
Joined: Fri Sep 28, 2018 12:26 am

### Re: 7E.3 in 7th edition

125-175=50
0.4(125)=50
The two ways of writing it are equivalent. You must be making a mistake elsewhere.

Ruiting Jia 4D
Posts: 65
Joined: Fri Sep 28, 2018 12:27 am

### Re: 7E.3 in 7th edition

aisteles1G wrote:the problem says "the presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 125 kj to 75 kj, by what factor does the rate increase at 298, all other factors equal?" I tried to do this using the Kr2/Kr1= e^-(Ea2-Ea1)/RT but keep ending up with the wrong answer than the solutions manual. The solutions manual for some reason does -(.4*125)/RT for the exponent instead of -(125-75kj)/RT and i cant understand why, thanks for any help!

Hi! Is this equation given to us on the sheet?

aisteles1G
Posts: 117
Joined: Fri Sep 28, 2018 12:15 am

### Re: 7E.3 in 7th edition

Ruiting Jia 4D wrote:
aisteles1G wrote:the problem says "the presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 125 kj to 75 kj, by what factor does the rate increase at 298, all other factors equal?" I tried to do this using the Kr2/Kr1= e^-(Ea2-Ea1)/RT but keep ending up with the wrong answer than the solutions manual. The solutions manual for some reason does -(.4*125)/RT for the exponent instead of -(125-75kj)/RT and i cant understand why, thanks for any help!

Hi! Is this equation given to us on the sheet?

Not exactly, this equation from the problem is just using the K=Ae^(-Ea/RT) equation for each K, which is on the equation sheet and you have to divide the Kr2/Kr1 and your A cancels out and you get the exponent with the two activation energies, so just remember to put the K2 one on top when dividing!

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