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A common question you can be asked when discussing the types of chemical reactions
is, what type of chemical reaction do you have
and/or how do you balance the chemical reaction?
So let's do a couple examples of these and I am just going to cover them.
So below you will see a chemical reaction written out for you,
and we are answering the question what type of reaction is it and what are the
prefixes or the coefficients that we put in front of it to balance it?
So we have aluminum plus oxygen makes aluminum oxide.
one thing that I like to do, one little trick,
that I like to use, is under my arrow,
I like to write out what my givens are
and you just list them out and then,
on the left-hand side of my givens, I like to write out how many I have.
So according to the left-hand side of my equation, I have 1 aluminum.
and 2 oxygen. On the right-hand side I have 2 aluminum,
and 3 oxygen. So even though I like to list
them out from the order I see them, oftentimes I have found in my experience, it's
best to balance oxygen first.
So the only relationship I know between a 2 and a 3
is that 2 times 3 and 3 times 2
both make 6. So I am going to start with that. I am going to put a
3 in front of my "O2" and then everything multiplies
So now I have got 6 oxygens on the left and I am going to put a 2
in front of my "AL2O3".
So now I have got 6 oxygens on the right. So that checks out.
now in the process i've changed the number of aluminum on the right
to 4, so what I can do now is put a
4 in front of my aluminums on the left
and then everything checks out and everything is balanced.
So my prefixes or my coefficients go
4, 3, 2. Let's do another one.
Oh, and what type of chemical reaction is this? Well,
having things together, I am synthesizing things together, so this is
actually a synthesis reaction.
Let's do another reaction here.
Here i've got "CH4" plus "O2",
yields "CO2" plus "H2O".
What type of reaction is this? Well, you know, anytime that you
add oxygen to something and carbon dioxide and water are produced,
that is your staple for knowing that you have a combustion reaction.
So let's go ahead and list out what we've got here. Like I said, I like to list out
what i'm given from left to right
but I don't always necessarily
balance it that way. So I have got 1 carbon on the left and 1 carbon on the right,
4 hydrogen on the left, 2 hydrogen on the right,
2 oxygen on the left and
3 oxygen on the right, so again
I'd really like to balance my
oxygen. You could balance in this case hydrogen or oxygen
first. Actually, I am going to do hydrogen first.
So to balance my hydrogen, i'm going to
put 2 in front of my
"H2O" and now i've got 4
hydrogen on the right and 4 on the left, so that's good and balanced now.
In the process, I have made my oxygen on the right
an even number instead of an odd number.
So that's a little happier. So 2 plus 2, i've got
4 oxygen on the right.
So to balance out my oxygen on the left, I am going to pop a 2 in front
here and get 4
and now everybody is balanced and happy. You can add little
ones in front if you want, but you don't have to. You have got a
1, 2, 1, 2 reaction here.
we could have balanced the oxygen first and got our
2 times 3 is 6 and you would have ended up seeing that you needed to reduce
but other than that, in this combustion reaction your prefixes
are 1, 2, 1, 2.