Chemical Forums

Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: tammx on December 16, 2007, 09:41:49 AM

Title: First order reaction, temperature and reaction rate constant?
Post by: tammx on December 16, 2007, 09:41:49 AM

Hi everyone!
I'm having trouble with this one:
At 55 degrees Celsius, a substance degrades by 75,2% in 10 minutes. This is a first-order reaction. What is the reaction rate constant (k)?

I tried to solve this using (1) k=1/t x ln(c₀/c_t), where t  - time, c₀=original concentration, c_t=final concentration=(100-75,2)% of c₀ and got k=2,32 x 10^-3

As I understand from my physical chemistry conspectus, formula (1) does apply for first-order reactions but I'm uncertain about not including the temperature.

Do I have to use the Arrhenius equation to find the solution, or is there a simpler way?
Thanks in advance for any hints at all!

Title: Re: First order reaction, temperature and reaction rate constant?
Post by: Hunt on December 16, 2007, 12:55:40 PM

Hello tammx ,
Your answer is correct but dont forget to include the unit of k : 1/s. The temperature is specified because k=f(T), so the temp must be included whenever the rate / k is determined or else the information/answer would be 'incomplete'.

Title: Re: First order reaction, temperature and reaction rate constant?
Post by: lemonoman on December 16, 2007, 01:46:45 PM

I just love that Vant_Hoff was the one to answer this question!  :)

But yeah, just to clarify, you have to say, "The equilibrium constant for this reaction at 55 C is 2.32 x 10^-3 s^-1"

Title: Re: First order reaction, temperature and reaction rate constant?
Post by: Hunt on December 17, 2007, 09:54:33 AM

lol... and I just love that lemonoman is still on the forums to cheer me up.

Title: Re: First order reaction, temperature and reaction rate constant?
Post by: tammx on December 22, 2007, 08:34:38 AM

Thank you for your advice!