Page 129 - Microsoft Word - LessonPlan-Overview.doc
P. 129
the rate of reaction because the A catalyst can also slow down a
properties of the substance has reaction. A catalytic promoter
ben altered.) increases the activity, and a
catalytic poison (also known as a
A higher concentration of the
negative catalyst, or inhibitor)
reactants increases the reaction
decreases the activity of a reaction.
rates because the number of
collisions increase. Catalysts offer a different way for
the reactants to become products,
Fine powders react more quickly
and sometimes this means the
than large chunks because there’s
catalyst reacts during the chemical
more area exposed to react when a
reaction to form intermediates.
substance is in powder form, so
Since the catalyst is completely
surface area plays a role in the
regenerated before the reaction is
reaction rates as well.
finished, it’s considered ‘not used’
To speed up a reaction without
in the overall reaction.
altering the chemistry of the
reaction involves adding a catalyst. Le Chatelier's Principle
A catalyst changes the rate of
This predicts how changes in
reaction but doesn’t get involved in
pressure, temperature, volume, or
the overall chemical changes.
concentration will cause a reaction
For example, leaving a bottle of to shift and compensate for these
hydrogen peroxide outside in the changes. For example, if the
sunlight will cause the hydrogen temperature of an exothermic
peroxide to decompose. However, reaction is increased, the
this process takes a long time, and equilibrium position shifts to use up
if you don’t want to wait, you can the heat by creating more
simply toss in a lump of charcoal to reactants.
speed things along.
In the reaction of colorless solution
The carbon is a catalyst in the of silver (Ag) with colorless
reaction, and the overall effect is solution of chlorine (Cl) gives a
that instead of taking two months white solution of AgCl:
to generate a balloon full of
-
+
Ag + Cl AgCl + energy
oxygen, it now only takes five
minutes. The amount of charcoal Increasing the temperature shifts
you have at the end of the reaction the equilibrium to the left,
is exactly the same as before it consuming some of the energy and
started. products to produce more
reactants. There will be less white
© 2010 Supercharged Science www.ScienceLearningSpace.com
531
