This content explains the fundamental principles of thermochemistry, focusing on how to measure heat transfer in chemical reactions and physical processes using calorimeters, guided by the law of conservation of energy.
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so what we're really interested in
chemistry is using thermochemistry and
measuring the kind of heat that it gets
transferred in our different kinds of
reactions or physical propert Pro
processes so we can have a couple of
definitions of things we want to study
so our system is what we want to study
else so we can look at our different
kind of systems we can first think about
our exothermic system and our exothermic
process so if we have a system that
we're studying which releases heat what
we're going to see in here is our heat
is going to go leave our system and go
into the surroundings of whatever is
there so you'll have lots of heat that
leaves out and we have some sort of cue
that's in there and what we can do is we
can measure the cue of our surroundings
for that exothermic process so after a
while what happens with an exothermic
process we're going to start out with a
certain temperature and as everything
gets uh re-equilibrated after the
reaction we should see the temperature
increase for an exothermic reaction and
the opposite thing happens for an
endothermic system so if we have some
sort of endothermic system heat from the
C surroundings are going to have to go
into the
system so this is really cool we'll
start off with a certain temperature and
after the reaction is done and it's kind
of equal out you we should see that the
temperature should actually drop for the
entire uh
calorimeter so this is a really good way
of measuring these kinds of reactions so
let me go ahead and show you two
different kinds of calorimeters that are
common in in the chemistry lab uh and
the first one looks really simple but it
is astoundingly precise in terms of its
measurements and this is what we call a coffee
coffee cup
cup
calorimeter and what we usually have is
some sort of Styrofoam cups you usually
have two of them and those act as
insulators so that we can isolate what
we're trying to study to inside of the
coffee cup and we put in there a
thermometer which measures the
temperature and we have some sort of
stir on it and we put a lid on it so
that heat doesn't leave the system and
so we can do a reaction that's inside of
the coffee cup and we can measure the
change in temperature based on the
thermometer of this reaction and it
works really well for a lot of the
different kinds of activities so we
typically put water in there we can
measure the temperature before and after
uh we do our activity and be able to
measure our um Heat or heat that's being
transferred another type of
calorimeter is what we call a a bomb
calorimeter and what a bomb calorimeter
does it keeps our volume very constant
so in the previous this is actually what
we call um a a uh we keep our pressure
uh constant so this is at constant
pressure in a bomb calorimeter we keep
this at constant volume so we actually
seal our reaction in inside of our bombb
calorimeter uh in here so we can have
this inner vessel that's inside we can
actually do a reaction in there that
doesn't um that can't see any kind of
water so then the cue of this what
happens inside of here goes into another
outer vessel that has um a liquid in
there so inside that liquid can actually
absorb and or release kind of um heat to
it and then the whole calorimeter will
have a a um a heat capacity to it so
whenever you see a bomb calorimeter you
will typically see a heat capacity for
the bomb
itself so we can differentiate between
the two different reactions but actually
the calculations for these aren't that
different between the two we can go
ahead and follow the law of conservation
of energy for both both of these kinds
of systems and uh how you navigate these
kinds of process is first realizing you
have to do some sort of calorimetry and
the main concept that comes out is this
law conservation energy and this law
conservation energy says we can't
create um energy we can only
transfer it so we have to read our
problems very carefully and look for all
the cues
so what kinds of cues are relevant to it
to that problem and the sum of all those
cues based on the conservation energy equals
equals
zero and so this gives us the kind of
concept that our Q of our
system which is what we're trying to
study and our Q of the
surroundings which is everything that's
not what we're studying has to equal zero
zero
so you will see this as Q of the
system equals Q of the surroundings but
what gets crazy in kind of thinking
about problems sometimes our
surroundings or our queue of the system
has multiple cues in there so I always
like to kind of think about it this way
and just take all of our cues and sum
them up and make them all equal to zero
because there's usually one thing in
there you're trying to study and you're
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