Law of Chemical Equilibrium and Equilibrium Constant Video Lecture - JEE

hi it's mr. Andersen and this is
chemistry essentials video 65 it's on
the equilibrium constant a chemical
weapon that was used in World War one
and killed a number of people as
phosgene phosphine is created through a
reversible reaction where you take
carbon monoxide and chlorine gas you mix
them together and you get this phosgene
and this is a world war two poster
warning people that this chemical might
be coming it gives off a smell kind of
like hay and since it's colorless that
was an important way for you to know
that this chemical might be coming and
so in any kind of a chemical reaction
like this it's reversible the reactants
are converted into products and the
products are converted back into
reactants but it's important that we
know do we have more reactants or do we
have more products and so we use our K
value or equilibrium constant to figure
that out in this chemical reaction at
standard temperature and pressure we're
going to have a really large K what does
that mean this reaction is going to move
towards the right that means that we're
going to have way more phosgene than
we're going to have any of these
reactants and so in a reversible
reaction reactants are converted into
products and back again and over time it
eventually reaches an equilibrium now
what is K K is simply a way to measure
when we reach equilibrium do we have way
more reactants or do we have way more
products that are being produced and so
I've got this model right here that
shows us how reversible reactions work
so there are going to be a bunch of
molecules over here we'll call those
reactants and they'll be green when
they're on this side of the chamber and
they'll be red when they move over to
the right side this is a pH e T
simulation over to the right I've
created a KO meter which is going to
measure our K value so K is going to be
the number of products divided by the
reactants at this case we only have
reactants on the left side and so we
have a very large number here a hundred
and how many products do we have zero
and so what's our K value going to be
it's simply going to be zero so let me
start this and see what happens to our K
value and so molecules are moving now
from their reactant to the product side
from the product to the reactant side
but we basically have the same level on
both sides and so our K values one now
as I tip it towards the right we're
getting more products and so that is
going to become a large
a number up here and so our value goes
up to three we have about three times as
many products likewise when we pull it
in the other direction now we have way
more reactants and since our reactants
in this case value is going to be around
seventy-five products around twenty five
our K value is going to be around a
third now this bottle oversimplifies a
little bit because we only have products
and reactants in this simulation in a
chemical reaction you're going to have
lots of products and lots of reactants
and so if we've got a reversible
reaction like this where this represents
our reactants and this represents our
products this is the general equation
for K but if we were to figure it out
for a more complex kind of equation this
is the general way that we write out K
where K represents the concentration of
one of our products so that's going to
be C raised to the power of the number
of moles that we have of that chemical
likewise if the concentration of D
raised to the power and that power is
going to be the moles of this product as
well likewise we're going to put the
reactants on the bottom is simply the
concentration raised to the mol so what
am I talking about let me show you an
example of that if this is our equation
right here this is going to be our
equilibrium constant and so what do we
have
well here's going to be our products on
the top so it's going to be the
concentration of water right here raised
to the 2 power because we have two moles
out in front of that likewise we've got
nitrogen gas raised to the 1 power
because we only have one mole of that
we're then going to put our reactants in
the bottom likewise both of these are
raised to the second power because each
of those have two moles now if I were to
give you that reversible phosgene
reaction could you write the equilibrium
constant for that what's our K value
going to be equal to it's simply going
to equal to this well each of these are
raised to the 1 power because we have
only one mole of each of these so this
would be our K value now we can
calculate K in the lab and so at
standard temperature and pressure
our phosgene is going to be this is
going to be that value I showed you at
the beginning four point five seven
times 10 to the ninth
what does that mean we're going to have
way more of this product than we do the
reactant at that given point in other
words you could write this number over
one on the bottom it's going to show you
how many of them are going to be the
FA's gene now if we were to change the
temperature we can actually change that
cave
you if I change that temperature to 200
degrees Celsius so if I change it and
make it a really high temperature you
can see that our K value is going to be
much lower what does that mean it's
going to be shifted back towards the
left and we're going to have way more of
those reactants than we do
products likewise if we were to take
this equation right here where we've got
nitrogen and oxygen and we're converting
that into nitrogen dioxide what would
that look like our K value our K value
is going to be simply this it's going to
be raised to the second power because we
have two moles of this gas what is our
teh value for this equation it's going
to be a really really small value what
does that mean that we're going to have
way way more reactants concentration
wise than products and so it's going to
be shifted way over here towards the
left side now what if I were to increase
temperature at this point let's say I
were to have a strike of lightning
that's actually going to raise our kya
value and it's going to push it over
towards the right side now we know that
in the atmosphere we have nitrogen gas
and we have oxygen gas but if we had a K
value that was really really large at
standard temperature and pressure
all of this would quickly be converted
into nitrogen oxide but we know that
doesn't occur it only occurs when you
have a huge amount of energy a huge
amount of lightning and so again in
summary if our K value is ever greater
than 1 that equation is going to move
from the reactants to the products side
we're going to have way more products
than we do reactants if it's ever less
than 1 then we're going to have the
reverse is true we're going to have way
more reactants than we do products and
so did you learn to use the values of K
to predict which chemicals we're going
to have when it reaches equilibrium I
hope so and I hope that was helpful