In this video we'll look at the difference between coefficients and subscripts.
The coefficients those are the numbers that go in front of compounds. Here we
have a two it's in front of the H2 or the two in front of the H2O. And this 2 this,
this coefficient, they apply to all of the elements the H's and the O's.
If we don't have a coefficient like with the O2 we assume that to be one.
Subscripts are different. They're smaller and they only apply to one element so this
two applies to the H is two applies to the O. We have a two here with the H and if there's nothing
written we consider there to be a one here. Subscripts are smaller and they kind of go
below the elements much like a submarine goes below the water. Let's just look at
one part of this equation here. Let's look at two H2O to understand the
difference between coefficients and subscripts. Let's start with the coefficient the large number
in front of the water molecule. This two means we have two H2O molecules . Two water molecules and
that they're separate and we could show that like this so in this sense the coefficient.
It's just a ratio or a number we have two water molecules we can write each one is
just H2O. A key idea is that when we have the coefficient we have our two water molecules
they're not chemically bonded. They're separate molecules. Now let's talk about the subscript.
When we look at the subscript in H2O. That tells us that we have two hydrogen's
one two and one oxygen and because these elements symbols right here are together they're chemically
bonded they are stuck together. Nnote that with our water molecule here there's nothing written after
the oxygen atom we assume that to be just one. So we have one oxygen atom in this h2o molecule
so pause for a second and try this.
With this two H2O here from our chemical equation how many total hydrogen and total oxygen atoms do we have?
So if we count them up down here with our two water molecules we have one two three four hydrogen's and one two oxygens.
We could also multiply two times two that would give us the four hydrogen's and then
one times the two to give us these two oxygen atoms. So pause and give this a try: how many
hydrogen atoms and oxygen atoms do I have when I have a coefficient of five in front of H2O.
You could count all of these up down here since we have five water molecules or you could say
2 times 5 that gives us 10 hydrogen's and 1 times 5 that gives us 5 oxygens. But keep in
mind they're all separate water molecules. The individual H2O molecules, they're not bonded together. It is
these two hydrogen's here forming the chemical bond with the one oxygen. Let's go back to our
original chemical equation. When we balance chemical equations we change the coefficients,
the numbers in front, and we do that so all of the atoms add up to be the same on each side. I have 4
hydrogen's here and I have 1, 2, 3, 4 here. I have 2 oxygens here I have 1, 2 here so in the chemical
equation we conserve mass. We didn't lose any molecules but they were rearranged and these coefficients
they help us make sure we have the right number. The subscripts may help us make sure we have the
right compounds. So let's take a look what would happen if we changed a subscript. So what would
happen if I was bouncing a chemical equation instead of H2OI changed the subscript 2 H2O2?
First off we have a very different looking molecule here and because we've changed its
molecular structure. It has different properties for example we drink water we're actually made
up of mostly water what would happen if you drank hydrogen peroxide nothing good that's
to be certain. In fact the hydrogen peroxide sold in stores is only about 3% the rest is water. If
you touched stronger hydrogen peroxide like 30% this is what would happen to your fingers. So we
can't change the subscripts once we change those subscripts we've made an entirely new
compound with different properties and when we're balancing equations we are
trying to make new compounds we're trying to get the ratios right between what we react together
in what's produced in the chemical reaction before. We wrap up here pause for a moment and think about
why we can't change subscripts but we can change the coefficients in a chemical reaction. If you
can't answer that question go back and watch the video again and make sure you understand
why. This is Dr. B with the difference between subscripts and coefficients thanks for watching.