Activation Energy Table
Date: October 2006
Hi, I have done an experiment looking at the
reaction between sodium thiosulphate and hydrochloric acid; now
by varying the temperature I have registered some data and made
an Arrhenius plot.
From this I determined the activation energy for the reaction to
be 52 kJmol^-1.
Now I have been looking ALL around for an accepted value, but have
Could you please help me by indicating either a source that
contains the accepted Ea or could you provide me with the value?
I found one source from which you might be able to compute their
value of the activation energy:
However, remember that the concept of activation energy is
empirical and a gross oversimplification of the temperature
behavior of most chemical reactions. There are several problems: 1.
The mechanism may involve several paths, and activation energy
assumes a single "simple" path. 2. There is a constant in the equation:
k = A*(exp^-Ea/RT) the so called "pre-exponential factor, A" which
is also a function (usually not known) of the temperature. 3. When
you plot the ln(k) vs. 1/T(kelvins) to determine Ea, the activation
energy you frequently find that the activation energy, Ea, appears
to be a function of temperature!! That is the plot isn't linear. And
even if it is linear it is not clear what it is you are measuring
because very complicated reaction mechanisms often produce simple
appearing concentration and temperature behavior.
Too frequently, all of the limitations of the concept of
activation energies are not spelled out for students. It's
empirically good for estimating the rate of a reaction at a
different temperature, but don't read a lot into its fundamental importance.
Click here to return to the Chemistry Archives
Update: June 2012