Hi. It's Mr. Andersen and this is chemistry essentials video 45. It's on catalyst classes
or the three different types of catalysts that we use. Catalysts are important in manufacturing,
in refining, in life in general. And they come in three different forms. We have acid-base
catalysts. So this sulfuric acid is going to be an example of that. We have surface
catalysts. And so this would be similar to the catalysts you're going to find in a catalytic
converter in your car. It's able to take carbon monoxide, this dangerous gas, and convert
it into carbon dioxide. And then enzymes are going to be another group of catalysts. And
those are going to run every chemical reaction inside a living body. And so catalysts can
be broken into three classes. We've got acid-base, surface and then finally we have enzymes.
How does an acid-base catalyst work? Well essentially it's going to take one reactant
and we're either going to add a proton to it or we're going to pull a proton away. And
as we do that that's going to speed up the reaction. A surface catalyst is generally
going to be made of metal. And if we can increase the surface area it's going to work better.
What it does is it increases the number of successful collisions in a reaction. And it
also can create new reaction intermediates or new steps in this overall reaction mechanism.
And then finally we have enzymes. Those are the biological catalysts. And what they can
do is also produce new intermediates or they can simply tug on a molecule and they can
lower its activation energy. So let's start with an acid-base catalyst. What these are
doing remember is adding a proton or taking a proton away from one of those reactants.
And here's an example of a reaction that is catalyzed by acid-base catalyst. We've got
isobutane and we've got propene. So these are going to found in just regular gasoline
or fossil fuels. But what we're doing in this step of refining is we're actually making
isooctane. And so we're make another hydrocarbon. And so if you ever fill up for gas and you
see that there are different levels of octane, what that really is a measure of the percent
of octane that we have or isooctane that we have in our gasoline. Well the higher that
number is, it doesn't give us more energy, but what it does is it allows our combustion
in our internal combustion engine to be more consistent. And so if we have really low isooctane
levels you can eventually experience what's called knocking in your engine. And it would
work better in a diesel engine for example if we have low octane fuels. And so what is
the role of this sulfuric acid? Sulfuric acid is going to donate a proton. So it's protonating
this propene. And as it does that it allows us to form this isooctane that won't normally
form on its own. How does a surface catalyst work? Well generally surface catalysts are
going to be made of metal. And if you remember metal, if we have a big chunk of metal, they're
going to share their electrons in a delocalized cloud around all of the atoms. But as we approach
the surface of that metal we're going to find that there are going to be unpaired electrons.
And so what you get are what are called active sites on the surface of that metal. And so
that allows the catalyzing of a reaction. In this case we have hydrogen gas and ethylene.
And what they'll do is they'll dock with a surface or the surface of that surface catalyst.
And that process is called adsorption. What does that mean? It's not absorbing into the
metal, it's adsorbing on the metal. And what it's doing is it's sharing and then pulling
electrons from one place to another. And so what you can get, in this case, these hydrogen
atoms can move around on its surface. And they're more likely to find a correct collision
with that original molecule. Same thing right here. And so what we can do on that surface
is we can catalyze the reaction. We're more likely to successfully produce that ethane.
And so the increase in surface area, if we make it a real fine powder or fine dust or
fine mesh we can actually increase these collisions even more. What's a great example of a process
that's catalyzed this way is the Haber process. So Fritz Haber is a notorious scientist. But
he came up with this Haber process. And in it what you're really doing is taking nitrogen
out of the air and we're making ammonia out of it. Now in life bacteria can do this. They
can take nitrogen out of the air. Put it into the soil. But without the Haber process we
couldn't do this on our own. And it's estimated that one-third of all the people on our planet
are eating food that's produced through this process. And if you look at it we've got a
number of different catalysts and a number of different containers. And you can see if
we look at all the elementary steps of this reaction there's a lot of adsorbing of the
gases, adsorbing of the nitrogen. And so eventually over time what we're doing is we're creating
ammonia. And here's the energy profile of that whole reaction. Last type is going to
be an enzyme catalyst. And so this is going to be a biological catalyst. It's found inside
our body. And so a great example would be the enzyme that breaks down sucrose. Sucrose
is simply going to be table sugar. And so if we look at it, it is a disaccharide. We
have two sugar molecules attached together. If we represent like that then an enzyme that
breaks that down would be called sucrase. And what's going to happen is the sucrase
will hold the sucrose. And what it does is that you have this fit where the enzyme kind
of wraps around it and tugs on that. And as it does that we can break that disaccharide
apart into its two monosaccharides. And everything in our body is going to be mediated through
enzyme catalysts like this. If you have a hard time breaking down lactose, it's because
you don't have lactase, that enzyme that can break it up. And so how do we control everything
in our body? It's through these biological catalysts that are made of proteins. And so
did you learn to explain changes in reactions arising from acid-base? Remember that's transfer
of a proton. Surface catalyst? Remember that's allowing those collisions to occur. Or enzyme
catalyst? Well if you did, you learned what I wanted you to. And I hope that was helpful.