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#### Violet89

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##### K = A * exp(- Ea / RT)
« on: February 24, 2013, 03:29:00 PM »

A first order reaction has an activation energy of 68.1 kJ/mol and a frequency factor (Arrhenius constant) of 1.48 x 1012 sec -1. Calculate the rate constant at 18°C.

K = A * exp(- Ea / RT)

I understand what to plug into this equation, but I keep getting the wrong answer. I calculate (- Ea / RT), press 2nd + LN, and multiply that by A. Am I doing something wrong?

I'd appreciate any help.
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#### argulor

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##### Re: K = A * exp(- Ea / RT)
« Reply #1 on: February 24, 2013, 04:55:00 PM »

Are you using R= 0.008314 KJK-1mol-1?
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#### sjb

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##### Re: K = A * exp(- Ea / RT)
« Reply #2 on: February 24, 2013, 08:19:21 PM »

Are you using R= 0.008314 KJK-1mol-1?
...or T=18, or a frequency factor of ~ 1500?
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#### Borek

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##### Re: K = A * exp(- Ea / RT)
« Reply #3 on: February 24, 2013, 10:04:24 PM »

I calculate (- Ea / RT), press 2nd + LN

On my TI that would mean calculating natural logarithm, not $e^{\frac {-E_a} {RT}}$.
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