Some combustion reactions tend to
involve fractions.
Oh no the dreaded fractions right? Now
I'm going to show you what to do when
you actually do have a fraction for an
unbalanced equation. So looking at this
unbalanced equation, the first step for
this, just identify how many of every
single element we have of our reactants
and of our products. So let's start right
then and there
identifying how many carbon hydrogen and
oxygen on our reactant side. So for
carbon we have 6, hydrogen there's 14
and oxygen there's 2 looking. On our
product side, Carbon we only have 1,
hydrogen we have 2 and oxygen, beware
of this, we have 2 plus this other one so
we have a total of three oxygen. Remember
you always want to leave oxygen for the
very very end whenever you're balancing
equations and also leave hydrogen for
the second to last. So I'm going to start
off with just balancing out the carbon.
There's 6 here, one on the product side
so we need 6 carbons on our product
side. I'm going to place a 6 in front
of this CO2 and remember you can't just
kind of like, let's say if you just
wanted to balance out the oxygen, you
can't put a 6 right in the middle of
our CO2 compound. We actually have to
keep it together since it is a compound.
So placing a 6 in front of that entire
compound of CO2,
note that this is kind of like you're
distributing and we now have 6 carbon
but let's recount all of those oxygen.
So 6 times that 2 would give us 12
oxygen plus this other one would give us 13.
So we now have 13 oxygen but still
only two hydrogen. Now that carbon's
balanced let's go down the list and
balance out our hydrogen. So in this case
hydrogen has 14 on the product side we
only have two so I want you to think of,
alright, what's gonna multiply by 2 to
give us 14 and that would give us 7
So 7 times this 2 would give us
14 hydrogen. So 14 hydrogen
however, once again this is like you're
distributing, 7 times, really a 1
subscript here, so there's 7 oxygen
plus that 12, so 12 plus 7 will give
us 19 oxygen. Yup you heard that right,
19 oxygen, and that carbon is still
balanced. So everything else is fine
except, no matter what we do there's
always going to be an odd amount of
oxygen on our product side. So that's how
you know you're gonna use a fraction.
With pretty much whenever there is a
time where oxygen or something else is
always going to be an odd amount of that,
that's when you use a fraction. What
we're gonna do is, since this side has 19,
then I'm gonna place 19 halves here.
That's where the fraction comes in. So
whatever odd-number you have, you're
gonna put a 2 underneath and this is
what we're gonna do to eliminate that
fraction as a whole. So your very last
step is to multiply all of your
subscripts by 2. So multiplying all of
your subscripts, what would happen is
we're actually gonna get a 2. We're gonna
get a 2 in front of that C6H14 and this
2 would cancel out with the 2 on the
bottom of your fraction just giving us a
whole number of 19 and we'll keep going
distributing that 2 to this 6 would
give us 12 for CO2 and lastly 2 times
that 7 would give us 14 for water and
that is our balanced equation using fractions.
