DRAFT: This module has unpublished changes.

Determination of Activation Energy    

 

            Once the order of the reaction is determined, if data is given for more than two

 

temperatures an Arrheneus plot can be made to determine the activation

 

energy. The following equations apply:

 

 

            In an Arrhenius plot the lnk is plotted against 1/T and a graph is obtained

 

with a linear slope that is equal to –Ea/R. Since the gas constant (R) is known to

 

be 8.314 J/mol*K and the slope is now know the activation energy can be easily

 

calculated.

   

 

Here is an example of an Arrhenius plot:

 

 

 

            For our particular example and for problems with data from only two

 

temperatures a more mathematical approach can be used to determine the

 

activation energy.

 

 

The second equation can be subtracted from the first to yield:

 

 

This equation can be rearranged to achieve an equation for the calculation for

 

the activation energy.

 

  

For our example the activation energy was calculated to be:

 

  

            Below is a view of the excel sheet for our particular example. The data in

 

purple and the time and change in pressure was given. Using that information PA

 

was calculated followed by a calculation of the natural log of PA and the inverse

 

of PA. The boxes in green are a linest function in excel in which the y values are

 

the natural log of PA and the x values are the corresponding time. The box in blue

 

is a calculation done to obtain the activation energy for this particular reaction.

  

 

 

 

DRAFT: This module has unpublished changes.