Today we're talking about when and how
to use a mole to mole ratio but first drink
your chemist tea.
 
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Now what is a mole to mole ratio? A mole to mole ratio is a conversion factor that allows
you to go from one compound to a
completely different compound. You know
to use a mole to mole ratio when you are
trying to change your compounds.
Now where do you find the numbers for that multiple ratio? In your balanced equation.
When you're balancing equations you have a coefficient in front of a compound or
a number in front of a compound. That is
what you use in a mole to mole ratio.
Let's try some.  How many moles of H2O are produced when 2.5 moles of O2 reacts
with H2. We're given 2.5 moles of O2 and
you're finding moles of H2O. Notice we're
going from O2 to H2O so we're changing
our compound. We have to use a mole to mole
ratio. Where we get that multiple ratio
is from our balanced equation.
Your setup will be with our given, first. That 2.5 moles of O2 on top aligning your moles
of O2 across from each other so they can
cancel and put what you're finding the
moles of H2O on top. Where we're going to take these numbers for our mole to mole
ratio is from the balanced equation. If
there is no original number
assume it's just a 1. There's one mole
and two moles of H2O multiply straight
across and you get 5.0 moles of H2O. Now I really want us to understand this
concept so let's do another example so
we could really master this.
How many moles of O2 are in 7.03 moles of CO2? We're given the
7.03 moles of CO2 and going to moles of
O2. We're changing the compound again so
we have to use our mole to mole ratio from our balanced equation. You're setup with
your given on top, the 7.03 moles of CO2. Aligning those moles
of CO2 across from each other so they
can cancel and placing the moles of O2
on top. Once again we'll get our mole to mole ratio from our balanced equation.
There are 5 moles of O2 per every 3
moles of CO2. Multiply straight across
and divide by 3 and you get 11.7 moles of O2.
Let's go ahead and put this into practice.
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