>> narrator: In this
Closer Look, we'll explore
mole to mole stoichiometry.
What is mole to mole
stoichiometry?
Mole to mole stoichiometry
is when there is
a balanced equation
and the objective is to convert
from moles of one substance
in a chemical reaction
to moles of a different
substance in that reaction.
Here's an example of
a stoichiometry problem
that involves
mole to mole conversions.
Hydrogen and oxygen gas
can be generated through
the electrolysis of water.
The balanced chemical equation
is two moles of water
decompose to form
two moles of hydrogen gas
and one mole of oxygen gas.
How many moles of oxygen
can be produced
from the decomposition
of 15 moles of water?
To start the problem,
take what's given
and put it in the upper
left hand corner
of the conversion chart.
In this one, there are
15 moles of water given
as the starting point.
The question asks
how many moles of oxygen
can be produced
from the decomposition
of those 15 moles of water.
So bring the units down,
in this case the moles of water,
and now use the mole ratio
from the balanced equation
to convert from moles of water
to moles of oxygen.
And notice there's a two
in front of the water,
and there's an understood one
in front of the oxygen.
So that means you put
a two in front of the water
and a one in front
of the oxygen.
Now cancel the units
of moles of water,
and the converting part
of the problem is finished.
Now all that's left to do
is to multiply
15 times one divided by two,
and notice the units
are moles of oxygen
which is what the question
asked for,
and so the answer will be
7.5 moles of oxygen.
There will be 7.5 moles
of oxygen produced
from the decomposition
of 15 moles of water.
This next problem involves
the reaction of sodium metal
and chlorine gas to form
sodium chloride.
And the question asks,
how many moles of
sodium chloride
can be produced from
nine moles of chlorine gas
with excess sodium?
So start this problem
like the other one.
Take what's given
in the problem, which is
nine moles of chlorine gas,
and put that in
the upper left hand corner
of the conversion chart.
Then bring the units down,
so put moles of chlorine
down here in the denominator
of the next box,
and you're converting
from moles of chlorine
to moles of sodium chloride.
These numbers can be found
from the mole ratios
in the balanced equation.
There's an understood one
in front of chlorine
and there's a two
in front of sodium chloride,
so put those numbers into
the conversion chart, here.
And notice the units of moles
of chlorine cancel,
and you're left with moles
of sodium chloride,
which is what
the problem asked for.
So to finish solving
this question,
multiply nine times two
divided by one,
which is just 18,
and you find that 18 moles
of sodium chloride can be
formed from the reaction
of nine moles of chlorine gas
with excess sodium.
Here's one for you to try.
This question is also
based on the reaction
that forms sodium chloride
from sodium metal
and chlorine gas.
It asks: how many moles
of sodium chloride
can be produced
from 4.13 moles of sodium
in excess chlorine?
Go ahead and pause the video
and try to work it
on your own,
and then press play
to check your answer.
Hopefully, your set up
looks similar to this one.
We took the 4.13 moles
of sodium which was given
to us in the problem.
And you should have put that
in the upper left hand corner
of the conversion chart,
brought the units
of moles of sodium down,
and converted
from moles of sodium
to moles of sodium chloride.
You found from
the balanced equation
a coefficient of two
in front of sodium,
so you put a two here,
And a two is the coefficient
in front of sodium chloride,
so you put a two here.
Notice the units of moles
of sodium cancel out,
and so you are left with
moles of sodium chloride.
To solve the problem,
you multiply 4.13 times two
divided by two and find that
4.13 moles of sodium chloride
can be produced
if 4.13 moles of sodium
react in excess chlorine.
That's a Closer Look
at Moles to Mole
Stoichiometry.
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