Hi. It's Mr. Andersen and this chemistry essentials video 55. It's on chemical and physical processes.
If I were to take this table salt and break it apart into sodium metal and chlorine gas
I'd be breaking those ionic bonds. And so this would be a chemical process or a chemical
change. However, if I were to take water and simply boil it, I wouldn't be breaking those
covalent bonds in the water molecule itself, I'd simply be pulling on those intermolecular
forces. Pulling on it enough so that I could get it to change from a liquid to a gas. And
so that would be a physical process. But there's a grey area in the middle. If I were to add
the salt to the water, it could either be a physical process as we dissolve it or a
chemical process. And so before we get to that we really have to understand the difference
between intermolecular and intramolecular forces. Intermolecular remember are going
to be between molecules. So between the yellow and the yellow would be an intermolecular
force. Those are going to be things like dipole-dipole forces, induced dipole forces. What are intramolecular
forces? Those are going to be within the molecule itself. Those are going to be the bonds, the
covalent and those ionic bonds. And so if we're looking at processes we can put it in
one of two categories. In a physical process what we're doing is we're breaking and forming
those intermolecular forces between the molecules. And so that usually ends up in a change of
state, from and solid to a liquid to a gas. In a chemical process however what we're doing
is breaking and forming those bonds. And so that's how we tell the difference between
these two processes. But there's a grey area in the middle. And in that grey area, if we
take an ionic compound and dissolve it in water those ions will be separated. And as
they're doing that we're not actually breaking those bonds, they're staying as an ion. We're
just moving those apart. And so you could argue that this is a physical process or a
this is a chemical process. And so let's start with a chemical process.
In a chemical process we're breaking those bonds. And so in the combustion of methane
we're combining it with oxygen. And you can see here that we're breaking those covalent
bonds. We're breaking the bonds between the carbon and the hydrogen and oxygen itself.
And so that's going to usually end up in producing changes in color, odor, gas, heat. Maybe precipitate.
This is a bunch of iron III reactions. And you can just see the remnants of all of these
in these reactions itself. You can see that we're breaking those bonds and then reforming
those bonds again. That's a chemical process. In a physical process however what we're doing
is simply pulling on those intermolecular forces that are holding the molecules together.
And that's just going to give us a change in state, like when we boil that water we're
heating up those water molecules. We're breaking those hydrogen bonds between the two. And
then we're starting to change it into a gas. And so in the grey area however we can take
something like water, which is a dipole. And we can start to separate all of the ions in
sodium chloride. So when you put salt in water it simply dissolves. Now are we technically
breaking these ionic bonds? No. We're not converting it back into sodium metal and chlorine
gas. What we're doing is just ushering them away. And so if we take that water, what it
really does is it surrounds the chlorine ions like this. And so what do we have? We have
this chlorine ion and it's attracted to the positive part of the water molecule. Or the
hydrogen portion of that partial charge. Likewise if we take that sodium ion it's going to be
the negative portion of the dipole that's actually going to usher that away. And so
you could argue that since these are intermolecular forces that this is simply a physical process.
But if you were to measure those bonds that you're breaking they're much harder than most
covalent bonds, and so you could argue that this is a chemical process. And so again,
did you learn to determine if this process is a chemical change, a chemical process,
a physical process or could be classified as both? I hope so. And I hope that was helpful.