This content explains how to calculate the heat released during a combustion reaction using a bomb calorimeter, considering the heat absorbed by both the water and the calorimeter itself.
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the other kind of calorimetry problem
that you will encounter is what we do
with a bomb calorimeter so typically the
words in the problem will say bomb
calorimeter in it so just remember it's
that sealed vessel that has all the
other um materials in there and the big
thing in there with a bomb calorimeter
you should have a Capital C which is the
heat capacity of the bomb
calorimeter so that should be somewhere
in the problem on here so what we're
doing in here is we are taking this mass
of glucose and we're burning it inside
of a bomb calorimeter so we are com uh
performing a combustion reaction so in a
combustion reaction it should be
exothermic so we should be releasing
heat the temperature of the calorimeter
increased from 23.8 De C to 35.6 De C
and then the calorimeter contains 775 G
of water and the bomb itself so here's
the key it has a heat capacity and look
at the units there 893 jewles per
degrees celsus so we know we have a
Capital C on here and now the question
is how much heat was produced by the
combustion of the glucose sample so we
need to go ahead remember the sum of all
the cubes are going to equal zero so
then we have to ask ourselves what are
the cues
that are in the problem so the Q in
there we have our Q the reaction and
that's the
combustion of the glucose so there's a
combustion that's happening there plus
we know that we have water in the
calorimeter plus there's going to be a
CU of the water because there's going to
be some heat transfer of the water
itself and then it tells us the bomb has
some sort of heat capacity so then
there's a
of the
calorimeter we're going to add all those
up to be zero so if we go back to what
is the system and what are the
surroundings this PE the reaction is
what we're
interested so that's our system
surroundings but I like to break it up
into the separate cues so we don't know
what our Q of the reaction is we can
calculate the Q of our water as the M
lowercase uh C delta T so that's our
Mass specific heat capacity and our
change in temperature and then we are
also told what the heat capacity of our
calorimeter is times delta T so our
change in temperature and how that will
all equal zero so this is what we want
to calculate we know that we have our
mass of our water is 700 75 G our c is
4.184 Jew per degrees Celsius G or
you'll see GRS per degree celsius and
our change in temperature is going to be
35.6 minus 23.8 Dees
C our Capital C on here is given to us as
as
893 jewles per de Cs and then we're
going to multiply that by our same
temperature final initial so our delta T
is 35.6 minus 23.8 degrees cus on here
so we can go ahead and calculate this
out our Q the reaction if we end up
calculating all of this out we should
38,000 300 jewles we calculate this out
over here
um and we should have
10,500 Jews we set that equal to zero so
we go ahead and add this up our Q of the
reaction plus
48,800 Jew equal 0 and then our Q of the
reaction should equal -
48,800 Jew and that should make sense to
us because we have a negative number we
reaction so we have a negative value it
makes sense in terms of the combustion
of our glucose and a lot of times what
we will do is we will actually uh report
these values in kilog so make sure you
look at your answer to see what units
you're going to use because you may have
to convert this as -
4880 jewles you might have to convert in k
k
there's one k for every 1,000 jewles I
never skip writing these dimensional
analyses so you will get a final number
of minus
48.8 K so you'll have to look at your
problem to see which value uh you might
be calculating whether it is kles or jewels
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