WEBVTT

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[MUSIC PLAYING]

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JESSICA HARROP: Hi, I'm Jessica.

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And today I'm
going to be talking

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about a chemical demonstration
I like to call the steaming gun.

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So you've probably seen
this before at the drugstore

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or in your house.

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It's called hydrogen
peroxide and it's

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the stuff you put on cuts.

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But it has many
other uses as well,

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from bleaching things
to powering rockets,

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depending on its concentration.

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The solution that you get at
the drugstore is usually 3%.

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So it's called hydrogen peroxide
and it's chemical formula

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is H2O2.

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So the atoms are
arranged like this.

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It sort of looks like
water, but the extra oxygen

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makes the molecule
more reactive.

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Now if you leave it
alone, it decomposes

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into water and oxygen. The
equation looks like this.

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I'm going to balance it.

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Now, normally, you
can't see this reaction

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happening because at room
temperature, it's very slow.

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But there are many
ways to speed it up

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like increasing the temperature
or adding a catalyst.

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In this demonstration
MIT's Dr. Dolhun

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uses a catalyst to make
the reaction go thousands

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of times faster than normal.

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Let's watch.

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JOHN DOLHUN: So we're going
to do this experiment here.

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And basically what we've got
is we've got four bottles.

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We're each going to do the
experiment in a bottle.

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We've got 15 mLs of
hydrogen peroxide here.

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And we're going to be
using a man-made catalyst.

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We're going to be using
manganese dioxide.

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And we're each going to
take a scoop of this.

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And we're going to put it in.

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You can set it down on the tray.

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And just-- it's
starting to work.

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You won't have to
stand up to see this.

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You can start to see some
condensed water vapor forming

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inside the flasks.

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Oxygen bundles are coming out.

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Now we're just going
to lightly hold that.

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Whew!

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JESSICA HARROP: OK,
so what happened?

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Dr. Dolhun had hydrogen
peroxide in the plastic bottle.

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Then he added a catalyst, some
manganese dioxide or MNO2,

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and got a plume of water vapor.

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So let's talk about
how a catalyst works.

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I'm going to draw
a potential energy

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diagram for this reaction.

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[MUSIC PLAYING]

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So here's my potential
energy diagram.

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So I've got potential
energy on the y-axis

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and the reaction coordinate,
or time, on the x-axis.

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The reactants are starting
at this amount of energy

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and the products
have this amount.

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Here, EA, that's the
activation energy.

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It's the amount of energy you
need to add to the reactants

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to make the reaction go.

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And delta H, that's the amount
of energy that's released

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when the reaction happens.

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Now let's see what happens
when I add a catalyst.

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[MUSIC PLAYING]

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With a catalyst, my activation
energy is a lot lower.

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And even a small reduction
in activation energy

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can make the reaction go
thousands of times faster

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than it normally would.

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But notice that regardless
of whether or not you

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have a catalyst, the delta H,
the amount of energy released

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in the reaction, doesn't change.

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So the catalyst only
speeds up the reaction.

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It doesn't change the
amount of energy released.

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Now, take a look at this.

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JOHN DOLHUN: Notice the
size of the bottles.

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These are very
exothermic reactions.

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The bundles have
basically shrunk down

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to a very, very
tiny size compared

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to the control bundles.

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JESSICA HARROP:
So as you can see,

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the catalyzed reaction
releases so much heat

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that it actually melts the
bottles and makes them smaller.

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Also, the catalyst
itself remains

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unchanged by the reaction.

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And designing
catalysts is actually

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a key subfield of chemistry.

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MIT's Richard Schrock
won the Nobel Prize

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working in this field.

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And remember how we
used H2O2 on our cuts?

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Well, we have an enzyme
in our bodies called

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catalase that does the same
thing as the manganese dioxide

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that Dr. Dolhun used.

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That's why when you put
hydrogen peroxide on a cut

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you see fizzing and bundles.

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The catalase in your
blood is breaking down

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the hydrogen peroxide.

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And according to recent
studies, low levels of catalase

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may play a role in the
graying process of human hair.

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If catalase levels are
low, it can't break down

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all of the hydrogen
peroxide in the blood.

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And that extra H2O2
starts to bleach your hair

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from the inside out.

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So to wrap up,
catalysts don't change

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the products of the
reaction or how much

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heat is released or absorbed.

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They only change the time
it takes for the reaction

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to finish.

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[MUSIC PLAYING]

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All right, that's
it for me today.

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I'll see you next time.

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