hello and welcome to the chemistry
solution this tutorial is on how to
calculate theoretical actual and percent
yields the theoretical yield is the
maximum amount of product that can be
obtained in a chemical reaction and we
calculate this from the limiting reagent
so the theoretical yield is something
that's almost never obtained you would
only obtain the theoretical yield under
perfect conditions where no product was
lost in the process the actual yield is
the amount of product that is actually
obtained from a chemical reaction and so
the actual yield is the amount of
product you would actually obtain if you
did this experiment in a lab and these
values must always be experimentally
determined so if you're doing a problem
involving theoretical and actual yields
the actual yield would always have to be
given to you it's not something you
could calculate looking at the balanced
equation where the theoretical yield can
be calculated using a balanced equation
and your actual yield can never be more
than the theoretical yield which just
means that you can't ever obtain more
product in an experiment then is
theoretically predicted using the
balanced equation the percent yield then
is a ratio of the actual yield to the
theoretical yield and you multiply that
by 100 to give you a percent let's go
ahead and look at an example if 16 grams
of caco3 are decomposed and 7.54 grams
of c a.o are obtained what is the
percent yield of c a.o obtained will you
remember from looking at our last slide
that the percent yield is always a ratio
of the actual yield over the theoretical
yield so in this problem 16 grams of
calcium carbonate is the amount of
reactant that we're starting with and
7.54 grams of calcium oxide is our
actual yield so the first step is that
you always need to check to make sure
your equation
is balanced sometimes you'll be given
balanced equations right from the
beginning and sometimes the designer of
the problem will expect you to balance
the equation on your own if we look at
this reaction will see that our equation
is already balanced one calcium atom on
each side three oxygen atoms and one
carbon atom on both the reactants and
the products side for the second step we
need to calculate the theoretical yield
of calcium oxide so like I mentioned
previously 7.5 4 grams of calcium oxide
is our actual yield and now we'll
calculate how much could theoretically
be obtained if the reaction was
conducted perfectly now remember we can
use the coefficients in our balanced
chemical equation to convert from one
reactant or product to another reactant
or product but remember if you're going
to do that you can only convert between
reactants and products if you're in
moles you can't convert directly if your
reactants and products are in grams so
we'll start this calculation with the
amount of starting reactant given in the
problem the problem says that we started
with 16 grams of calcium carbonate now
to convert between calcium carbonate and
calcium oxide we need to first convert
calcium carbonate to moles and we'll do
that using the formula weight which is
100 point 1 grams of calcium carbonate
per mole of calcium carbonate and we put
grams on the bottom because those are
the units that we want to cancel out now
that we have moles of calcium carbonate
we can convert to moles of calcium oxide
using the coefficients in our balanced
chemical equation and this is why it's
very important to check that your
equation is balanced in this case one
mole of calcium carbonate will give us
one mole of calcium oxide this allows us
to cancel out moles of calcium carbonate
and leaves us in moles of calcium oxide
but we want to calculate our percent
yield and because our actual yield is in
grams we need to calculate our
theoretical yield in grams so next we'll
convert from moles of calcium oxide to
grams of calcium oxide using the formula
weight of calcium oxide which is 56
point
in grams of calcium oxide per mole this
allows us to cancel out moles of calcium
oxide and gives us a theoretical yield
of 8.9 seven grams of calcium oxide we
now have our theoretical yield and we
can calculate our percent yield by
taking our actual yield given to us in
the problem remember the actual yield is
something you can never calculate on
your own it must be given to you divided
by our theoretical yield and when we
multiply this value by 100 to get a
percent
we'll see that our percent yield is 84
point one percent so what you may have
noticed is that theoretical yield
problems aren't that much different from
problems you've probably already been
working converting from grams of one
reactant or product to grams of a
different reactant or product except
this time we're just taking it one step
further and calculating our theoretical
yield which is what you've been
calculating all along and comparing that
to a supposed actual yield that was
obtained in a lab to give us a percent
thanks for watching the chemistry
solution we hope you enjoyed this
tutorial
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