Catalysis
and Activation Energy
Introduction:
In many chemical reactions a catalyst is needed in order to
get the reaction going. When MnO2 is added to hydrogen peroxide,
a very exothermic and rapid chemical reaction takes place.
This reaction liberates water, oxygen and heat, as shown below.
Without the MnO2 catalyst, this
reaction does not occur at an appreciable rate. This is a very
visual reaction that is carried out in a two liter plastic
bottle.
Another very visual reaction is one involving the combustion
of methanol vapor/ air. This reaction again liberates water,
but as the reaction below shows, carbon dioxide is also given
off. Without a spark or flame, this reaction does not go because
of the high activation energy.
These two reactions can be discussed in terms
of the activation energy and its effect on the rate of a chemical
reaction. This concept can be related to many practical observations
such as catalytic converters in automobiles exhaust systems
and the fact that most things around us ate unstable with respect
to combustion. In order to get these reactions started, either
some energy or a catalyst is required.
|
