Enthalpy's state function property allows for the calculation of reaction enthalpies by summing the enthalpies of stepwise reactions, as demonstrated by Hess's Law.
Mind Map
클릭해서 펼치기
클릭해서 인터랙티브 마인드맵 전체 보기
so one of the advantages thinking about
our enthalpy as a state function is that
we can start to add things together uh
between the different reaction so that
concept is from hess's law and this is
totally due to the fact that it's a
state function for enthalpy so it the
process of enthalpies can be written as
a series of independent stepwise
reactions and the enthalpy change for
all of it is the sum of all the enthalpy
changes in all of the
reactions so here's an example of
thinking about hess's law so we want to
determine the enthalpy of formation of
iron Tri chloride so thinking about how
we want to calculate that and we are
given these two steps and what we can do
is we can do some sort of manipulations
of this so first of all we need to go
ahead and WR the reaction for the
formation of iron chloride so we know
that the enthalpy of formation for the
reaction is we are going to form one
mole of iron chloride and we are going
to form this from the elements at its
standard state so we know that we have
iron as a solid in here and we know
chlorine uh exists as a datomic gas but
how many chlorines do we actually need
so if we think about this we only need
three so if we think about our leish
structure looks something like this we
only need three out of the four so
that's three Hales of a
chlorine of chlorine
molecules so how do we actually
calculate this so this is now our Delta
H knot this is written as a formation we
are given these two fundamental steps um
uh up here so one and two what can we do
to actually manipulate them and add them
together and in this case it's actually
relatively straightforward we notice
that we have a product of fe2 over here
and we have one of them on this side of
the equation and lo and behold if we
take both of these equations and we just
add them up we see that we have an iron
on this side we have have an iron over
here we have one chloride plus a half of
a chloride this gives us our three Hales
chlorine and um our iron over here and
if we look on the product side if we add
this up this iron uh D chloride ends up
being canceled on both sides and we have
iron Tri chloride so for this we can
take our hess's law that our heat of
formation is going to be the sum of
these two over there and if we add up
the some of these we end up getting -3 99.5
99.5
K so that is the final answer for this
reaction so that is a fairly
straightforward kind of hess's law where
you can just kind of add it up the only
tricky part was go was writing this kind
of um enthalpy of formation and that was
just by the definition of what a
formation reaction actually
is and the next part is we will go
through something a little bit more complicated
텍스트나 타임스탬프를 클릭하면 동영상의 해당 장면으로 바로 이동합니다
공유:
대부분의 자막은 5초 이내에 준비됩니다
원클릭 복사125개 이상의 언어내용 검색타임스탬프로 이동
YouTube URL 붙여넣기
YouTube 동영상 링크를 입력하면 전체 자막을 가져옵니다
자막 추출 양식
대부분의 자막은 5초 이내에 준비됩니다
Chrome 확장 프로그램 설치
YouTube를 떠나지 않고 자막을 즉시 가져오세요. Chrome 확장 프로그램을 설치하면 동영상 시청 페이지에서 바로 자막에 원클릭으로 접근할 수 있습니다.
