Drawing particulate models of reaction mixtures | Chemical reactions | AP Chemistry | Khan Academy

- [Instructor] In a previous video,

we used a particulate model like this

to understand a reaction,

not just to understand the reaction,

but to balance the
chemical reaction as well.

And when I hand drew these particles,

the atoms in this particulate model here,

I tried to draw it pretty close

to their actual relative sizes.

Carbon atoms are a little
bit bigger than oxygen atoms,

and they're both a lot
bigger than hydrogen atoms.

What we're gonna do in this video

is extend our understanding
using a particulate model

to start to visualize
what actually might go on

in a mixture

of some of these reactant molecules.

So what I have here on the left-hand side

are the various molecules.

I have two methane molecules here.

I have three water molecules.

And what I wanna do with you

is draw what we would expect
to see after the reaction.

And I encourage you, like
always, pause this video

and see if you can have a go at that,

maybe with a pencil and paper,

at least just try to
imagine it in your head,

before I do this with you.

All right, now, let's do this together.

Now, we know that for every
methane and every water,

we're going to produce one carbon monoxide

and three molecular hydrogens.

And each of those molecules of hydrogen

have two hydrogens in them.

So let's just say that this
one and this one react.

They're going to produce
one carbon monoxide.

I'm gonna try to draw the
relative sizes roughly, right?

So one carbon monoxide.

And then they're gonna
produce six hydrogen atoms

that are going to be in
three hydrogen molecules.

So let's do,

that's two and four,

and then I'll just do one here

and then six.

All right, so I took care
of this one and this one.

And now we can imagine that
maybe this water molecule

reacts with this methane molecule,

and so that would produce
another carbon monoxide.

Let me draw that

roughly at the right size.

Another carbon monoxide molecule

and three more hydrogen molecules

for a total of six more hydrogens.

So that's one and two

and three.

And now we have this water right over here

that had no one to react
with in this situation,

had no partner.

And so that's just going to be
a leftover reactant molecule.

So let me just draw it right over here.

So that water could be

right over right over here.

And so this was a useful way

of starting to visualize
what might be going on.

Remember, this is happening
at a very high temperature.

They're all bouncing around, et cetera.

And then when they react,
you might get this,

but then this water molecule
has no one to react to,

so it is, you could view it as a leftover

after the reaction.