Hi. It's Mr. Andersen and this is chemistry essentials video 44. It's on catalysts. Catalysts
can speed up a reaction but they're not consumed in the reaction. One of the greatest chemistry
demonstrations is elephant toothpaste. And I'm going to put a link right here to a video.
This is from Brian Swarthout, a friend of mine. And his son Sam is doing the elephant
toothpaste demonstration. Essentially you add a catalyst to it and then you have this
reaction go really, really quickly. And so please give that a watch. Brian makes some
wonderful videos in chemistry and physics. I'll put a link to some of his stuff down
below. But how do catalysts work? Well essentially they speed up a reaction. Some catalysts will
actually slow down reactions, but in general they're going to speed it up by lowering the
activation energy. The amount of energy we have to put in a system before we can stress
those bonds, break them and form new bonds. And so it has to go through this transition
state. But a catalyst can stabilize that transition state. And therefore it can lower the activation
energy and it can speed that reaction up. Now some catalysts will actually add new intermediates.
In other words they're going to add new steps in this overall reaction mechanism. And so
if we look at the energy profile of a reaction remember we've got reactants on one side and
products on the other. This would be an exothermic or an exergonic reaction. And so essentially
we've got reactants. We've got products. But if we want to move between the two we have
to add a little bit of stress to those bonds. In other words we have to achieve this transitional
state. Eventually we can break those bonds and we can form new bonds. And so let me show
you a catalyst at work. This is catalase, which is an enzyme found in almost all living
cells. So what I'm doing is adding a little bit of hydrogen peroxide to a bag. It's got
yeast in it. And you could try this at home. Shake it up a little bit and you can see I'm
producing a huge amount of oxygen gas right there. And so hydrogen peroxide would do this
on its own, but if we add an enzyme to it we can speed that whole process along. So
how does it do that? If we look at the reactants on the left, it's going to be hydrogen peroxide.
And the water and oxygen on the right. We see that we have to get through a large activation
energy. And so what does catalase do? Well scientists think there's a heme group in the
middle of it. And that means just, it's a number of atoms. But it's got iron right in
the middle. And what that iron is acting to do is to pull one of those oxygens away. So
it's stressing that bond on the hydrogen peroxide. It's stabilizing this transition state so
it's more likely to fall into that just water and oxygen. Again it's going to release energy.
But if we look at the energy here and we look at the energy here, the net amount of energy
that we're getting out is going to be the same. That a catalase is just acting to lower
the activation energy. Now sometimes it works by creating new intermediates. And new steps
in the reaction. And so in this elephant toothpaste experiment, you're taking concentrated hydrogen
peroxide and soap. And then we're adding potassium iodide to that. And that's simply going to
act as the catalyst. Now what's it doing? That iodide is going to grab one of the oxygen.
So it's going to make this intermediate which will then bond with the other hydrogen peroxide.
And that's going to produce water and oxygen. And so we're really breaking a one-step reaction
into two steps. And then we've got a new intermediate here. Well what does that look like on an
energy profile? This would be our original energy profile. We've got reactants on one
side, products on the other. But if we look at this two-step process what we're doing
is we're actually lowering the overall activation energy by doing two steps. In the first step
we're freeing up that oxygen. Then we're bonding it to the other hydrogen peroxide to make
water. And so we've lowered the overall activation energy of that reaction. And so did you learn
to translate energy profiles, that's what this is right here, particulate representations,
and then even symbolic representations for chemical reactions with and without a catalyst?
I hope you did. And I hope that was helpful.