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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Violet89 on February 24, 2013, 09:29:00 PM

Title: K = A * exp(- Ea / RT)
Post by: Violet89 on February 24, 2013, 09:29:00 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.

Title: Re: K = A * exp(- Ea / RT)
Post by: argulor on February 24, 2013, 10:55:00 PM

Are you using R= 0.008314 KJK^-1mol^-1?

Title: Re: K = A * exp(- Ea / RT)
Post by: sjb on February 25, 2013, 02:19:21 AM

Quote from: argulor on February 24, 2013, 10:55:00 PM

Are you using R= 0.008314 KJK^-1mol^-1?

...or T=18, or a frequency factor of ~ 1500?

Title: Re: K = A * exp(- Ea / RT)
Post by: Borek on February 25, 2013, 04:04:24 AM

Quote from: valerie232323 on February 24, 2013, 09:29:00 PM

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

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