we have here if you have heterogeneous
system in equilibrium what is that means
that
some of the reactants or the products
are at different phases when we simply
say different phases like solids
- solutions or liquids these are simply
if you have solids and the gas that
would be heterogeneous or liquid and
will be written as such that you leave
out the solids or pure liquids that
involved in the equilibrium expression
and as we explained last time we don't
really leave them out because their
concentrations are one Wooler
because their concentrations are
constant in the solid state or constant
in liquid state but if you have
solutions molar concentrations in fact
in solutions they change those are the
one only that we will have taken into
account and also the gases if they have
a gas phase you should take account of
gases to such an equilibrium here
decomposition is of the calcium
carbonate given solid calcium carbonate
given calcium oxide solid and carbon
dioxide gas if you write down the K sub
C for this it would be directly equal to
the concentrations of carbon dioxide
above the solid calcium carbonate and
the KP if we write down the KP for this
reaction again it would be equal to the
pressure partial pressure of the carbon
dioxide again at equilibrium again
remember we don't write down the
concentrations of these solids not the
reason that their concentrations are
equal to one but they are constant they
actually included in this constant pair
so we just give one equilibrium constant
okay oh we can't
concentrations again we will work out
using an example first it says tabulate
all known initial and equilibrium
concentrations you just follow these
steps it would be very easy to carry out
and find out the concentrations at the
equilibrium concentrations are known
calculate the change says and use the
balanced equation to find the change for
all other reactants and products use the
balanced equations and write down the
concentration changes for all others
again that involved in the equilibrium
and the fourth step is use the initial
concentrations and changes to find
including concentrations of all species
and the last step is calculate the
equilibrium constant using the
equilibrium concentrations again if we
know the equilibrium concentrations we
can calculate the equilibrium constant
as we said before or if you know the
equilibrium constant and know the
initial concentrations for example then
we can calculate the concentrations of
all the species okay let's look at the
example here a closed system initially
contained in that mole simply hydrogen
gas and that mole of iodine at 448 again
degree centigrade allowed to reach the
equilibrium the concentrations of the H
I is one point 87 times 10 to the minus
3 molar calculate the case of C at 448
degree centigrade for the reaction
taking place which is the equilibrium
reaction this is actually the
equilibrium reaction and we will
calculate the equilibrium constant for
this now what given again the initial
concentration of the hydrogen and iodine
both are in gaseous form now the
temperature is also given and we asked
to calculate the temperature at this
actually the equilibrium constant at
this temperature
this reaction again the only effect of
the temperature is remember when the
temperature changes the equivalent
constant is changing we're not going to
use the temperature here to calculate
the equilibrium constant but we have to
report the equilibrium constant at that
specific temperature actually that's
important okay let's look at the next
step again here this is a this is very
easy but if you just use step by step
and solve your problem like we do here
in fact it would be very easy so you
have the equations actually balance
equations then you have here a table
which says the initially that means
these are simply we call the initial
concentration of the reactants or
product whatever we have the species
that means before we simply before the
system reaches to the equilibrium an
issue we start with that concentrations
in this case the concentrations of the
hydrogen in fact gas is 1 10 to the
minus 3 molar and the concentrations of
i2 is again this molar two times at the
minus 3 molar and the initial
concentrations of H I is zero right
because we only start with the hydrogen
and the iodine again in the gas phase
now changes we will put the changes here
again it says that the final
concentrations of the H I is one point
eighty seven times 10 to the minus 3
molar this is the H I increased by one
point eight seven times 10 to the minus
3 molar and then the other
concentrations let's look at the
concentrations of the others actually b9
35 times 10 to the minus 5 and this is
935 times 10 to minus 4 and at
equilibrium again you calculate that the
equilibrium concentration will be six
point five times ten to minus five and
106 five times seven minus three and
this is given again here this is given
so we calculate the equilibrium constant
but
look at let's go to the previous slide
here so we have this h2 gas and plus i2
gas and equilibrium to hydrogen iodide
again gas and what is actually given us
the initial concentrations of these
species and the concentrations of H I at
equilibrium again you see it says
analysis of the equilibrium mixture
shows that the concentrations of H I is
187 10 to the minus 3 so if we just go
to the next here the concentrations of
this is 1.8 7 times 10 to the minus 3
molar
I should probably that's okay and now
once we I know the concentrations of
this in 8 1 8 7 times 10 to the minus 3
molar initial concentrations of this is
given as 1 point 0 0 0 times 10 to the
minus 3 molar right and this one is 2
point 0 0 times 10 to the minus 3 molar
again now if this is the let's put it
over here at the beginning this is 0
initial concentrations and the change of
the concentrations is given for the
actually H I and that is I can write
down here 1 point 8 7 times 10 to the
minus 3 molar then I can calculate the
concentrations of these the change of
the concentrations of these here that
would be equal to what let's let's put
that here
change and equilibrium right and I will
put over here equilibrium 87 times 10 to
the minus 3 molar also at equilibrium is
given now how once actually this is
given and those concentrations are given
I can calculate the change here the
change here will be what we respect to
this it will be half of the H I
concentration at equilibrium right why
because this reaction simply says that
when one mole of H I
reacts half am actually 2 moles of H I
will be produced when one mole of h2
reacts and this means two moles of H I
will be produced and the same thing is
here when mole one mole of iodine
reacted then I will have two times of
that two moles of H I so that means that
the change here is equal to the half of
this which is 1 point 8 7 times 10 to
the minus 3 molar and this one is also 1
point 8 7 times 10 to the minus 3 molar
clear yes don't you yeah / - actually
this is the change okay now the initial
equilibrium concentrations this one is
given so what will be the equilibrium
concentration this number minus this
change right and that is again
calculated here as given 9 point 35
times 10 to the minus 4 this is going to
be 9 no let's put that we this will be
actually six point five times 10 to the
minus 5 molar and this is going to be
one point
note 10 to the minus 5 bollard this will
be 1.0 6 5 10 to the minus 3 molar at
1.06 5 times 10 to minus 3 molar and
this is the equilibrium concentrations
actually is given let me see okay what
is alright this is initial
concentrations and this is the change
and if you just subtract it by 2 and
yeah subtract that number from this I
will have no the subtract that by 2 will
be 9.30 5 10 to the minus 4
mrs. 9.10 2 minus 4 these here six point
five times ten to minus five is obtained
by subtracting this from this right so
again the initial concentrations the
equilibrium concentrations of hydrogen
will be found by taking the initial
concentration and subtracted this change
actually that's equal to this and this
one taking this number and subtract it
from the initial concentration this is
the occlusion concentrations and once
those are given we can calculate the
equilibrium constant because the only
thing we have to do is just put them in
equations here this is the equilibrium
expression K sub C and the concentration
square of the concentration is H I
divided by the concentrations of h2 and
i2 and put the concentrations
equilibrium concentrations of these from
the previous table then we find out that
the equivalence is equal to the 51 this
is the game very very simple very simple
but you just have to do write the
balanced equation and find out the
initial concentration changes in
concentration to reach the equilibrium
and the equilibrium concentrations once
you have the equilibrium concentrations
then you can calculate the equilibrium
constant now this is another important
concept is that is it says is a mixture
equilibrium which way does the reaction
go this is simply means is this the
equilibrium constant for this K sub C
equals 51 right act what was the
temperature 400 something 448 degree
centigrade at 448 degrees centigrade now
the question is is this if I simply have
concentrations of h2 equals to one point
zero times 10 to the minus 4 molar and
concentrations of i2 equals to 3 point 5
times 10 to the minus 6 molar and the
concentrations of H I let's say equals
to the two point zero times 10 to the
minus 4 molar like this so I mix them
all these are initial concentrations
initial concentrations initial
concentrations the hydrogen is 1 0 times
10 to the minus 4 molar I 2 is 3 5 times
10 to minus 6 molar H I is 2 point 0
times 10 to the minus 4 molar and all at
448 that means degrees centigrade now
the question is there are three
possibilities actually the first is is
this system is at equilibrium is this
system at
now the second question is is if this
system is not at equilibrium which way
the net reaction will take place to
reach to the equilibrium to the right or
to the left
remember again if you simply have a
mixture of the reactants and the
products for a chemical reaction if the
system is at equilibrium there will be
no net change to the product side or
reactant side that means no net reaction
will take place but if the reaction is
not at equilibrium that means those
concentrations are not at equilibrium
then the system will reach to the
equilibrium always if the system is not
an equal agreement will reach to the
equilibrium but to reach the equilibrium
it may go from reactant to the product
or it may go from the products to the
reactants side now can we find out
whether the system is at equilibrium
first second is whether the reaction
will go net reaction will proceed to the
right to reach the equilibrium all to
the left to reach at equilibrium now for
a case like this what we do again is
this we let's look at this slide here
says we calculate the reaction quotient
now what is a reaction quotient reaction
quotient is actually the same expression
as the equilibrium expression but the
concentrations of the species does not
do not have to be necessarily the
equilibrium concentrations right so Chu
is equals to again I if I write it for
this it would be equal to H I
concentration raised to the power 2
divided by h2 concentration and then
times the i2 concentration like this
okay but now if these concentrations are
the equilibrium concentrations then Q
is equal to equilibrium constant
now if again how we find out we just put
it there that means if Q is equal to K
sub C right
that means if I put the values here and
find out that it's equal to equilibrium
concentration EQ is equal to equilibrium
that means the system is at equilibrium
right system let's say is at equilibrium
now if Q is greater than K sub C that
means reaction quotient right there is
greater than K then to reach the
equilibrium that means that the Q should
be decreased
now how can i decrease Q by increasing
the concentrations of these decreasing
the concentrations of that what does
that means that means the system will
shift to the left right that means
decreasing the concentrations of that
increasing concentration of that system
will shift to the left there will be a
net reaction to the left need to reach
the equilibrium now the third
possibility is if Q is less than K sub C
then the reaction will proceed in as
such a way to make the Q equal to K sub
C so that means it will increase the
case of see how the K sub C will be
increased by increasing the
concentrations in nominator decreasing
the concentrations in denominator what
does that means the reaction net
reaction will be from left to the right
to reach to the equilibrium clear very
very simple again very simple so let's
see in this case if I just put the
values here let's put the values here
see let's see if you can calculate that
each eye is two point zero times sin 2
minus 4 and squared right and divided by
1
point zero times sent the minus 4 molar
hydrogen and this one is times 3.5 times
10 to the minus 6 here and this would be
equals to let's see if I can calculate
it now this is going to be 4 times 10 to
the minus 8 right
and this is going to be simply 3.5 times
10 to the minus 10 right so the result
would be let's say if this is let's make
that 4 or okay let's that would be again
about 1.0 times 10 to the 2 this is
about that means is equal to hundred
right so which way the reaction will
take place again if I if I start with
these concentrations the coup is much
greater than K sub C right because the K
value here is 51 and the Q I calculated
here is hundred greater than K sub C
when Q is greater than K sub C the Q has
to be decreased decrease in Q means that
the reaction has to go from right to the
left
decreasing the H I concentration
increase in the others this is what how
we apply it let's see I guess this has
the same thing so Q looks like the
equilibrium constant K but the values
used to calculate it are the current
concentrations not necessarily those for
equilibrium as I said if they're at
equilibrium actually Q will be equal to
K sub C the equilibrium constant to
locate Q 1 substitute the initial
concentrations of reactants and the
products into the Kalu expression this
is what we have done that means to find
out where the Q is right we calculate
the value of Q to compare it
and from that again if two is equal to
the K that means the system is at
equilibrium
now if Q is less than K nature will make
the reaction proceed to the product side
to make the Q larger and make it equal
to K and if Q is equal to K the reaction
is actually at equilibrium this says
natural wants that Q is equal to K what
does that means that means if you leave
the system alone it will always reach to
the equilibrium right that's what nature
wants Q is equal to K means so as I as
we said Q is equal to K means the
reaction is at in equilibrium if Q is
greater than K and then in our case Q is
greater than K sub C and the reaction
will proceed in the reverse direction to
lower the kick to and make it equal to K
sub C okay yeah this clear very simple
again very very simple now calculating
equilibrium concentrations again if you
know the equilibrium constant and if you
know the initial concentrations of the
reactants for example or the
concentrations of the product and the
reactant which is not at equilibrium or
not equilibrium we can calculate the
concentrations of the species at the
equilibrium so if you know the
equilibrium constant you can find the
equilibrium concentrations from initial
concentrations and changes it says you
will set up a table similar to those
ones used to find the equilibrium
concentration it's always useful to make
that table set up that table actually
but the change in concentration row will
simple be a factor of X based on the
stoichiometry let's see how we apply it
here again on the same equilibrium
system an example a one liter flask is
filled with one mole of h2 and two moles
of i2 at 448 degree centigrade given
that K sub Z is equal to 50 points
five at four four eight degree
centigrade what are the equilibrium
concentrations of H 2 I 2 and H I
actually again sometimes these type of
problems involves calculations you know
you know sometimes times taking
calculations but simple math actually
not more than that just takes time but
the best way to do that again is it says
set up this table like this and the
initial concentrations and the change in
concentrations and equilibrium and
concentrations over here again you see
since the flask the volume of the flask
is one liter and we have two mole of i2
and one mole of h2 that means what molar
concentrations of h2 is 1 molar right
and the molar concentrations of i2 is 2
molar because you just divide the number
of moles by the volume in liters it will
give you the molar concentrations so
these are the molar concentrations here
1 0 0 and 2 0 0 molar concentrations and
now the change of this again would be as
follows if minus X mole molar amount of
h2 is reacted then minus X molar amount
of a I 2 will react with it what does
that mean that means the change in the
molar concentration then in that case in
H 2 will be minus X minus means it will
be reduced that much and the molar
concentration change in I 2 will be
minus X the same amount now what will be
the molar concentrations of H I actually
change in molar concentrations of H I
since this is zero at the beginning as
you see here when one mole of that
reacts two moles of H I produced that
means that the concentration change in H
I at the equilibrium will be plus two x
two times of that now why it is plus
because plus simply
indicates increasing in concentration -
indicates the change in decrease in
concentration and at equilibrium again
we write down the equilibrium
concentrations if this is the change
then the equilibrium concentrations of
hydrogen will be the initial
concentrations of hydrogen which is 1
molar minus X and this is two molars
minus X and this will be 2 X since at
the beginning we didn't have any and now
we put it in the equation equilibrium
expression and solve equation for X it
will be a quadratic equation and we have
to solve the quadratic equation again
and this is the equilibrium expression
now these are the equilibrium
concentrations in terms of initial
concentrations and in terms of changes
that we simply call that X actually and
the equilibrium concentration of the
product 3 X 2 squared - x hydrogen
iodide and this is the equilibrium
concentration starting with this - X
this is the minus X again 2 minus X and
this is equal to this so we take this
part and solve it solve it for X and
this is going to be a quadratic equation
remember the quadratic equations as you
probably know from the calculus as minus
b plus/minus square root for AC b square
minus 4ac divided by 2a know that
formula then you calculate the X but you
have to be careful again here since this
is quadratic you will find out two
values for X X is unknown here right now
usually one of the value doesn't have
any meaning because if you just put that
X for example this value of x in the
equilibrium expression here since this
is 1 and subtract 2.3 to 3 from that the
number will be minus and the same thing
will be also true here - - and that's
not right you know that the
concentration or change in concentration
and
not be greater than the initial
concentration there's no amount of the
reactant that we have there changes so
this is you just throw out this and this
is your answer to the questions so the
concentrations of the species at
equilibrium we have to calculate that
that is the value of x actually the
concentration will be found by
subtracting the initial concentration
from the initial concentration
subtracting the X the concentration at
equilibrium for hydrogen is 0.065 molar
and the same way the concentrations of
i2 is one point six five molar and this
is 1 point eighty 7 molar very simple
very very simple once you set up your
problem and see the changes and write
down the equilibrium concentration in
terms of initial concentration and the
change of X then you can solve the
problem all right now
Lucia tell your principal is also very
very simple if you understand what it
means here it says if a system at
equilibrium is disturbed by a change in
temperature pressure or concentration of
one of the components the system will
shift in his equilibrium position so as
to counteract the effect of the
disturbance what does that means first
of all this simply means suppose you
have an equilibrium system let's simply
take this reaction again gas plus i2 gas
equilibrium H I gas - this is in a
closed system at equilibrium now if you
disturb the equilibrium
and let the system alone again the
system will reach to the equilibrium
again but it will not be the issue we
could probably the values of the you
know concentration values may not be the
initial concentrations of or initial
equilibrium concentrations I should I
should say and how can you disturb the
equilibrium system as it says here you
can change the temperature this is let's
say at 448 degrees centigrade right so
if you change the temperature of the
system let's say 490 degrees centigrade
that means it will be disturbance that
means that that temperature the system
will not be anymore at equilibrium but
what will happen if you let it alone it
will reach to the equilibrium okay now
another way of doing it type change in
the pressure these are all gases and
there is any actually this is in a
closed system so there's going to be a
total pressure of the system due to the
partial pressures of hydrogen and iodine
and hydrogen iodide there will be
partial pressures of that but there will
be a total pressure actually now how can
you change the pressure of this closed
system
if you add yeah if you add Noble get a
noble gas neon for example nothing will
happen
doesn't matter how much you simply add
because when we say the change in
pressure means the change in pressure of
the system due to these gases or change
in the partial pressures of one of those
actually alright so how can we change
the pressure yes that's all it is by
change in volume if you increase the
volume total pressure due to these it
will decrease but if you decrease the
volume then the total pressure will
increase now the third is the
concentration changes that means I can
simply change the concentrations of
these how can I do that
simply remove some from the system or
add more to the system at equilibrium
again these are all disturbance that
means if you have done one of these that
the system is not anymore at equilibrium
and it will reach the equilibrium this
is what it says now how it will reach to
the equilibrium I guess this is probably
difficult to read it but let's let's
start with the concentration but let me
see it I guess I have to go back because
the most important thing is here it says
now the system he this this part is
reported the system will shift it is
equilibrium position so as to counteract
the effect of the disturbance this means
whatever you have done to disturb the
system the system will try to counteract
that what does that means in terms of
concentration is let's take the first
concentration suppose that I add some
hydrogen gas to this system at
equilibrium from the outside what does
that means I increase the concentrations
of the hydrogen
so the system will try to counter act
that effect that means it will try to
decrease that concentration how can it
do that by shifting the equilibrium
because it will shift to this direction
right until what until the equilibrium
is really all right now suppose that
again at equilibrium I remove Aitu from
the system that will be equivalent or
saying reducing the concentrations of I
to iodine right now
the system will try to increase the
concentrations of that now how the
concentrations of i2 can be increased in
this system if the equilibrium shifts to
the left right and that will increase
until what until the equilibrium is
established new equilibrium is
established right again now this is the
concentration change now how about we
simply if I add H I to the system it
will shift this way if I remove H I it
will shift that way again increase in
the concentration the system will try to
decrease it if you decrease the
concentration the system will try to
increase now pressure wise let's look at
the pressure if I simply decreed
decrease the volume of this system that
means that the total pressure will
increase so the system will try to do
what to reach the equilibrium it will
try to decrease the total constant total
pressure how can it decrease the total
pressure in this case shift in which way
the total pressure will decrease to the
left or to the right it will not change
yes exactly it will not in this case it
will not change but if I have let's say
this system h2 gas + + o2 gas to h2o
yes I guess all right in this case I
guess this is correct right get that
correct in this case if I have a system
like that decrease in the volume and
increase in the pressure then which way
it will go this way or that go that way
to the right right it will go why
because by shifting the reaction to the
right in this case will decrease the
number of gas molecules in that valley
right decreasing the number of gas
molecules or number of moles of gas
molecules means the pressure will
decrease the pressure will decrease and
that's that's again the case if I
increase this value then the reaction
will shift the pressure will be
decreased and the reaction will shift
backwards because two moles of gas will
produce actually three moles that means
it will shift that way but if the number
of gas molecules as in this case on the
left and on the right are the same the
change of pressure or the change of
volume will not affect the equilibrium
system in this case there will be no
effect on the equilibrium system now how
about the what is left here temperature
right now remember when temperature
changes the equilibrium constant changes
right equilibrium constant changes so by
changing the temperature how the system
will counteract that depends on whether
your reaction is exothermic reaction or
endothermic reaction right now this one
here exothermic reaction exothermic
reaction what does that means that means
Delta H is less than zero
that's what exothermic means right so
here if I simply increase the
temperature what does that means I'm
increasing the total energy of the
system so it will try again this is in
terms of kinetic energy you can think
about that in terms of kinetic energy so
the system will try to decrease it how
the total kinetic energy and energy
actually will be decreased by simply
shift in this way because the reaction
going that way means that the heat will
be absorbed from the surroundings right
surrounded so again the change of the
equilibrium constant with temperature
depends whether you're exothermic
reaction or endothermic reaction in this
case as T increases for exothermic
reaction KC decreases you can put it
that way for exothermic reaction but for
endothermic reaction and the thermic
reaction where Delta H is greater than
zero now increase in the temperature
will also increase the equilibrium
constant right so what does that means
that means for exothermic reaction at
equilibrium right if you simply increase
the temperature the reaction will shift
from the product to the reactant side
for the anatomic reaction increase in
the temperature simply the product will
shift just the other way around the KC
will increase from reactant to the
product again this is what the look
should show your principal are all about
that is the effect of temperature effect
of pressure by change in volume or
effect of concentration by change in the
concentrations of the reactant or the
product in equipment okay I guess let's
see if I have more all right
I guess we will leave it here let's have
a break ten minutes