we're talking about chips free energy
and how we get to this point remember
when we talked about the entropy change
the entropy change of the universe is
equal to the entropy change of the
system and the surrounding we only know
these and then we substitute the
surrounding entropy change of the
surroundings with minus enthalpy change
of the system divided by the temperature
for spontaneous and constant pressure
and we get this and rearranging it
finally equation here so minus T Delta s
universe is equal to enthalpy change of
the system and temperature minus
temperature times entropy change of the
system now by looking at this again if
the process is spontaneous remember
irreversible spontaneous processes are
River irreversible and the entropy
change of the universe according to the
second law of thermodynamics will always
be positive right now that simply means
that if the process is simply
spontaneous this part here the Alta ash
universe will be positive multiply that
by an minus T that means this part on
the left side of the equation will be
negative now what does that means that
means the reaction is spontaneous now if
this part actually minus T Delta s
universe is not negative that means that
the reaction will not be spontaneous so
in other words as I said last time if we
know the value of this here and then we
can calculate for a process we can
simply predict whether the process will
be spontaneous or not spontaneous and
how we simply obtain that if we know the
enthalpy change of the system and the
entropy change of the system we can put
those here and calculate this and if
that turns out to be negative this where
the process is spontaneous if that turns
out to be positive the process is non
spontaneous
now instead of talking about minus T
Delta s universe that has been simply
replaced by another thermodynamic
function which is simply called JYP's
free energy gibbs free energy and this
is designated
by capital G again just like same as the
enthalpy and the entropy the Gibbs free
energy is a state function what that
means that the Delta G change in the
Gibbs free energy in fact will be
independent of the path followed to go
from initial to the final state as
spontaneous as simply the state function
and then we can simply write this
equation here which is JYP's free energy
change Delta G is equal to Delta H times
T Delta s so some way if we can
calculate simply the values of Delta G
from here then we can predict whether
the process will be spontaneous or
non-spontaneous if the Delta G turns out
to be negative we say the process is
spontaneous now if Delta G turns out to
be simply positive in that case we say
the reaction is written way or the
process is not spontaneous
you
predicting
sponsored each
again from the chemistry standpoint I
will simply use this equation to predict
whether a chemical reaction will be
spontaneous or it will be non
spontaneous and that's very very
important information so we simply have
this equation and if we can calculate
Delta H and Delta s again we can simply
find out what the reaction will be
spontaneous or non-spontaneous again you
see the important things is the
spontaneity of a process is determined
by two factors one is the enthalpy
change of the process second is the
entropy change of the process now
sometimes these two changes entropy and
the enthalpy effect is in the same
direction sometimes they are in opposite
directions right when they are in the
same direction that means that depending
on their sign the process will always be
spontaneous or will be always non
spontaneous but if they are opposite to
each other that means that if Delta G
Delta H is negative and Delta s is
negative also
direction that means not the way it is
written but it will be in the reverse
direction again so now three
informations dependent on the values of
the Delta G for the process spontaneous
non spontaneous or equilibrium again if
this is equal to zero Delta G is equal
to zero that means in equilibrium now
here is the how we this is the reaction
actually between nitrogen and hydrogen
Haber process how the reaction to obtain
the ammonia again free energy change is
given here as the reaction goes from
reactant to the product so this is
actually the free energy of the reactant
and this is the free energy of the
product so the free energy difference
here will be simply this minus that
whatever that value is but now you see
again the free energy of the system as
the reaction goes to the right decreases
like this and that becomes minimum here
and that increases here but this
actually corresponds to react in one
mole of ammonia with three moles of
hydrogen to obtain two moles know one
mole actually from the beginning against
one mole of nitrogen react in one mole
of nitrogen with three moles of hydrogen
gas and to obtain two moles of ammonia
and the in the the change free energy
change actually is between this point
and that point that much here but you
see again as the reaction goes from left
to the right the free energy decreases
decreases and becomes minimum here and
then if you push it all the way to the
right again that means reactant one mole
of nitrogen with three moles of all of
hydrogen to obtain two moles of ammonia
then we get to this point now this
is the point where we have the
equilibrium actually and that is the
point where delta g correspondence delta
g corresponds to zero right there now at
this point if you simply take the
concentrations of the reactants and the
products put it in the equilibrium
expression you will find that it will be
equal to the equilibrium constant so
this corresponds the minimum Delta G
there corresponds to the equilibrium
State
for this reaction okay this is another
standard free energy change again
analogous to the standard enthalpies of
formations are standard free energies of
formations this is again we also have
standard free energy of formation for
the chemicals for the substances we use
in reactions as a matter of fact just
like the enthalpy of formation the free
energy of formations is also equal to
zero for pure elements under standard
States but all others will have a free
energy of formations just the same as
the enthalpy of formation the Delta G F
0 which is a free energy of formation
corresponds to the free energy change of
the reaction in which the compound is
obtained from its pure elements under
standard conditions under standard
conditions so what does that means that
means we can simply make a table
determine the standard free energy
change of all substances all chemicals
and make a table now we will use those
we can use those just we use the
enthalpies of formation to calculate the
free energy change of a reaction
actually just like we did calculated the
enthalpy change of a reaction by using
the enthalpies of formation of the
reactants and the products again so this
is again just shows how the change in
the free energy during the chemical
reactions we start from here from the
reactants the free energy of the system
decreases
Croesus decreases and that becomes
minimum and this is the equilibrium
again and it comes to here that means
converging all the reactants this this
actually corresponds convert in all
reactants to the products right so the
free energy change will be between this
point and that point here as a matter of
fact so reactants products and the
equilibrium that corresponds to the
equilibrium again now let's examine how
the sign changes actually I should say
the sign of the enthalpy change and the
entropy change of a process allows us to
predict whether the reaction will be
spontaneous non spontaneous or
temperature dependent spontaneity right
this is the very simple table again you
see again here we will consider this
right and just we try to find out what
will be the sign of Delta G will be
positive or negative that's all we are
looking for now for a reaction for a
chemical reaction if the enthalpy change
is negative what does that means that
means the reaction is exothermic right
exothermic and if the entropy change is
positive that means increase in entropy
now what does that means this is
positive here this is negative here when
you multiply this minus T positive value
here that means this value which is
Delta G will always be negative right so
what does that mean that means for a
process where Delta H is negative and
Delta s is positive that process will be
spontaneous at all temperatures always
spontaneous right now another case here
and if the Delta H is positive here and
Delta s is
decreasing in the entropy so what does
that means this is positive and this is
negative negative times negative will be
positive and this whole thing's here
Delta G again will be positive what does
that means that means that the process
will be not spontaneous
at all temperatures doesn't matter what
the temperature is you can't really
change the spontaneity by changing the
temperature because it will always be
positive again for the process which
have Delta H positive Delta s negative
there then again the third possibility
is if the enthalpy change is negative
and if the entropy change is also
negative in that case let's look at here
now this is negative right and now this
is also negative what does that mean
that means multiplying this by negative
T here this part will be positive this
one this part will be negative now to
have the Delta G to be negative actually
this part should be high and that part
should be simply low now how can we make
that part low numerically again that
means if P is low then T Delta s will be
low and that this term here will be
positive that means the positive term
will be low and the negative term will
be higher than that numerically right
absolute values and that leads to a
negative Delta EIJ what does that means
that means if Delta H is negative for a
process Delta s is also negative this
process will be spontaneous at low
temperatures but will be non spontaneous
at high temperatures right that's what
it says just analyzing this again taking
that equation mathematically put the
values now the last possibility the
fourth possibility is if Delta H is
positive and Delta s is also positive
now what does that means this part here
is positive this is positive and you
multiply it by
negative that means this is negative so
what to make that Delta G negative that
means this has to be high right and what
does that means if Delta s is not
independent of the temperature again
then at high temperatures the process
will be spontaneous because Delta G will
be negative but at low temperatures
again the process will be non
spontaneous non spontaneous so these are
the possibility but remember we simply
assume in this case that the enthalpy
change of a chemical reaction or a
process and the entropy change of the
chemical reaction or a process are
independent of the temperatures is this
correct I mean yes actually we can say
yes not exactly though I mean the
enthalpy change and the entropy change
will also have some temperature
dependence but it will be very very
small and for the wrench of the
temperatures we study we can assume that
we did actually assume that the enthalpy
change and the entropy change of the
process or reaction is independent of
the temperature so that by change in the
temperature we can change the Delta G
value even we can change the sign of the
Delta G value what does that means that
means if a reaction is not spontaneous
at a certain temperature we can make it
spontaneous at another temperature
depending on whether the Delta H and
Delta s positive or negative the sign of
those right so that's very very useful
again informations as a matter of fact
okay now let's try to see how the
equilibrium is related to the free
energy change of a chemical reactions
now under any conditions standard or
non-standard the free energy
change can be found this way okay by
using this reactions doesn't matter
standard or not standard so the Delta G
in fact for a process is equal to Delta
g0 that is this standard free energy
change that simply means that the free
energy change of a chemical reaction
under standard condition and standard
condition means that the gases partial
pressure are all one atmosphere and the
concentrations of the species in
solution will be one molar that's what
it corresponds to standard State Delta
g0 plus RT Ln Q now R is the gas
constant again we know and T is the
temperature in Kelvin
this is the natural logarithm of Q is
the equilibrium quotient right for the
process equilibrium curve for the
process now here it says under standard
condition concentrations are 1 molar so
Q is equal to 1 and in Ln Q will be
equal to zero what does that means under
standard conditions Delta G will be
equal to Delta G zero right because
that's what the standard conditions is
this part will be equal to zero that
drops out okay now at equilibrium at
equilibrium the Q in fact equilibrium
quotient will be equal to the
equilibrium constant now remember at
equilibrium the free energy change is
equal to zero right so that means that
this is Delta G will be equal to zero so
if you just replace those in this
equation over here then the equation
becomes this part is zero equals to
Delta g0 and plus RT Ln simply K this is
the equilibrium constant equilibrium
constant now rearranging that again
Delta G zero is equal to minus RT Ln Q
or K is equal to this what does that
means that means that if I know the
standard free energy change of a
chemical reaction I can
calculate the equilibrium constant for
that reaction at a given temperature
whatever the temperature is we just put
the values here and you calculate the
equilibrium constant very very very
practical actually right now
the question is how can I calculate the
Delta g0 now the Delta G zeroes is
calculated from the I guess this is the
last part from the standard free energy
change no it will be calculated from the
free energy of formation of the
reactants and the products and those
free energies of formations are given in
fact in equations let's see I guess I
should have it somewhere here yes this
is for the entropies but we also have
that for the free energy of formations
in other words let's let's give you an
example let's say delta g free energy
standard free energy change for a
chemical reaction will be equal to sum
of the n times Delta G 0 F for product
and minus some of the M Delta G zero for
the reactant so these values actually
the free energy of formations for the
products and free energy of formation
for the reactants are all given as a
table so we take those table just like
same as the enthalpies of formations or
the entropy in fact we can calculate
this standard free energy change for a
chemical reaction now once we calculate
that state
free energy change then we can calculate
the equilibrium constant right as we see
here we can calculate this equilibrium
constant and that's a very very
important informations on things okay
now in other things which can be simply
used if I know the enthalpy change of a
chemical reaction and if I know the
entropy change of a chemical reaction
from here I can simply find out whether
the reaction will be spontaneous or
non-spontaneous by calculating Delta G
again right now if the reaction is not
spontaneous then I can also calculate
the temperature at which that reaction
will be spontaneous right by changing
this T again I can find out at what
temperature the reaction will be
spontaneous so let me just show you I
picked up an example from the book and
let's work it out and see how we simply
predict at what temperature the reaction
will be spontaneous right spontaneous
and the question is chapter 19 and 109
just picked up end of chapter problems
and it says at what temperature is the
following reaction is spontaneous at
what temperature is the following
reaction spontaneous
okay now what is the reaction reaction
is this Iren oxide this is iron to iron
three oxide actually this and plus two
carbon now carbon is solid and graphite
and goes to carbon dioxide gas and plus
ayran solid this is actually reduction
of the ayran or to iron metal right to
get the iron metal as a matter of fact
in the productions of iron and it says
at what temperature it will be
spontaneous first of all we have to find
out whether the process is spontaneous
or not spontaneous right how by
calculating the Delta G now how can we
calculate the Delta G first we calculate
the Delta H and then we have to
calculate the Delta s right now where we
get those values from the tables
actually their standard states given at
the end of the book actually we have
those appendices which lists all the
enthalpies of formations entropies
standard entropies and standard free
energy of formation for the compounds so
let's let me just put it over here give
you the values so we have we need these
iron 304 solids and here let's put the
standard enthalpy of formation x' and
this is kilojoules per mole and here
let's put the standard and
P a number again we don't put Delta
there because it's the standard entropy
because every substance has an entropy
at a certain temperature only
crystalline pure perfect crystalline
substances that zero Kelvin has zero
entropy right now the unit here is
joules per mole per Kelvin like this so
I have to go to the table and then find
out what are the enthalpies of
formations and the entropy is here now
one thing is very important the state of
each reactant is very important you have
to clearly indicate what state the
reactants and the products are why
because when you go to the table to find
out the standard enthalpies of
formations or standard free energy
formations or entropies again there
these states are important if they are
solid they have a different value than
if they had liquid or a gas
right so for example here it says the
solid now Carman solid has a diamond
form and the graphite form and also
fullerenes remember that's another form
so here if you just put solid is not
enough because shall I look up the
diamond entropy or shall I look at the
graphite entropy both are solid carbon
right solid carbon so here it says
carbon graphite so you look at the table
with the carbon graphite and write down
the values let's write now the values
this one is one thousand one hundred and
seventeen point one minus kilojoules per
mole and entropy for that is 140
six point four again now the second one
is carbon solve solid and graphite all
right what is this value again remember
the elements when they are pure at their
standard state the enthalpies of
formations is zero now the question is
what is this standard state for carbon
it is solid but is it graphite or
daimond graphite graphite is the
standard state for carbon so we look at
the graphite and that is this simply
means that will be equal to zero I don't
have to look for that right because it
will be zero actually the table gives
all three values and if it's zero it
puts there 0 but in the exam for example
we may not give you the value of this
not this form you know you're supposed
to know that that the enthalpy of
formations of graphite will be zero now
the enthalpy the entropy of graphite
again you see again it's not zero even
in the standard elemental form and the
values are five point ninety six okay
then we have carbon dioxide gas this is
again the standard state for carbon
dioxide a gas and the and the free
enthalpy of formations is minus three
hundred and ninety three point five and
the entropy is standard entropy to
thirteen point six the last is ayran
solid and here again it is the standard
state solid ayran that means this is
going to be equal to zero and this is
27:15
okay now I will calculate first Delta H
zero right now we're from the enthalpies
of formations the sum of the products
minus sum of the reactants so let's put
over here carbon dioxide so I have two
carbon dioxide that means I have two x
minus three hundred n ninety three point
five plus three times what zero right
because it's zero there and then this is
the product then minus the enthalpy of
formation of the reactants right and we
take this here which is going to be
minus one thousand one one seven point
one this is the negative value and here
coefficient is one don't take that and
then is the graphite and two x plus two
times zero because the graph is standard
then we calculate this when we calculate
it put the values and let's see what I
found I found plus three hundred and
thirty point one now the unit is very
important that's another things when you
simply find and as a result in a problem
if it has a unit you have to show the
unit what is the unit the unit is
kilojoules just kilojoules know per mole
because I multiplied them by the number
of moles that they appear again their
coefficients right so that is just
kilojoules then I calculate the Delta s
zero exactly the same
you just take the entropy off the
product standard entropies off the
product and two times two hundred and
thirteen point six and plus three times
twenty seven point fifteen there's no
none there's no zero values here right
they're all non zeros this is the
product and minus the reactant one
hundred and forty six point four plus
two times five point sixty nine and then
we calculate that when we calculated it
will be three hundred and fifty point
eighty-seven now what is the unit the
unit again is joules per Kelvin there's
no mole
multiplied by mall because here these
are actually a number of moles we
multiply them right so that is going to
be joules per Kelvin okay now now you
can tell me whether this reaction will
be spontaneous at low temperature high
temperature or it will always be
spontaneous or will never be spontaneous
Delta H is positive and Delta s is also
positive what does that means at what
temperature low temp actually the
reaction is not in the category of
always spontaneous or always non
spontaneous from that we can simply say
that that is what actually at low
temperature it will be non spontaneous
because Delta G will turn out to be
positive but at high temperatures it
will be spontaneous because Delta G will
turn out to be negative right now the
next question is at what temperature
that spontaneity change
can we calculate it and the answer is
yes we can calculate that too
because what we are simply looking for
so here Delta G let's write it Delta G
now this is equals to Delta H now I can
write it zero here because I assume that
the enthalpy change is independent of
the temperature in this case so I can
put their standard enthalpy change
wouldn't make any difference but here I
don't have to put standard enthalpy
change there and T and Delta s 0 like
this ok now what I want is at what
temperature Delta G will be negative
right
first of all let's find out at what
temperature Delta G will be zero right
and actually I can simply find our Delta
G will be equal to 0 at Delta H 0 T
Delta s 0 and from here I can find out
the temperature as simply Delta H 0
dependent by Delta s 0 right and I just
take that put it on this side and
divided by Delta s 0 now let's put the
values here the enthalpy change for the
process that we calculated is 330 point
15 but the unit is kilojoules the unit
here is joules I have to do I have to
change either kilojoules to joules or
Joules to kilojoules it's better to
change I guess
kilojoules to joules and leave this Jule
here joules per Kelvin now to make that
joules I have to multiply it by three so
this is joules right and divided by the
Delta S which is three hundred and fifty
point eighty seven and this is also
joules per Kelvin the unit and the
results will turn out to be as let me
see nine hundred and forty point eight
Calvin
somewhere about seven hundred degrees
centigrade right 700 degree centigrade
now so the reaction I can say the
reaction will be spontaneous
at T greater or smaller sometimes it's
smaller sometimes it's greater it will
be greater because as we have seen there
in that equations they too have that
party Delta as larger as negative T has
to be high so the reaction will be
spontaneous at temperature greater than
simply 940 point 8 Calvin so this is the
answer ok so you see how we can use the
thermodynamic data to find out
spontaneity of a chemical reaction and
actually find out the temperature at
which range the reaction will be
spontaneous or will be non spontaneous
yes any questions yes
yes you can you can you can simply say
that because when Delta G is equal to
zero that means that the reaction is at
equilibrium no no you can't there is no
spontaneity
when you have an equilibrium it's a
reversible process remember it's a
reversible process reversible means
equilibrium so we're looking for
spontaneous process it may be
spontaneous in the way it's written or
spontaneous in the way reverse
directions right if it is zero it's an
equilibrium right equilibrium then you
can actually find out again to make it
negative in fact how the temperature
should change right to change the
equilibrium constant yes okay I guess
now let's start the next chapter
now actually I can I can calculate the
equilibrium constant right if I know the
Delta g0 in fact any temperatures at
this temperature I can calculate that
this will be actually Delta g0 calculate
the equilibrium constant there too
now the chapter that we will cover
actually is a teen chapter previous
chapter than the thermodynamics but it
doesn't have anything to do with the
thermodynamics now it's about the
chemistry of environment chemistry of
environment now this is really very
important chapter particularly like if
you start thinking about the life on the
earth and how it's possible and what are
the processes are taking place in the
atmosphere right now particularly
chemical reactions what kind of chemical
reactions are taking place here the
atmospheric chemistry is very
interesting actually as a matter of fact
now first of all we have to remember
that the life on Earth is possible due
to three things right one is the energy
that comes from the Sun now second is
the atmosphere that around the earth
right which actually supports the life
we have the gases that we inhale ate and
actually mean and the third is what
water water very very important that is
the actually those three things that
makes the life possible and the earth
makes the life possible on the earth now
in this chapter we will look at the
atmosphere and how it changes and what
are the chemical reactions are taking
place in the atmosphere and what are the
processes actually that protect us from
the hazardous things that will take
place on
the earth actually that helps us to live
on this earth as a matter of fact right
but what we should simply remember also
that due to the human activities on the
earth the ik logical system the original
ecological system of the earth is
changing and if we don't take any
precautions about this the human means
actually the humans not taking any any
precautions to prevent this the life of
living things on the earth will be
doubtful let's say after thousand years
or five hundred years or I don't know
maybe three hundred years right so very
very important to be conscious about
that realize this and take the
precautions accordingly to prevent that
happening as a matter of fact okay now
the atmosphere again have different
layers or they just you know classify
the atmosphere starting from the earth
surface up to the sky and actually here
we have four layers of the atmosphere
one is the troposphere this is on the
earth again and it goes up to ten
kilometers from the earth up to ten
kilometres some books it will say like
twelve kilometres actually there's no
strict rule there saying that exactly
ten kilometers or exactly eleven it may
be eleven twelve kilometers and that's
it and then we have the stratosphere
again all at the end we have spheres
right and and that goes from about ten
kilometers up to fifty kilometers and
then from there from fifty kilometers up
to about 85 kilometers we have
mesosphere and then we have the
thermosphere about 85 kilometers and
this goes up
- 700 kilometers 700 kilometers now from
700 kilometers not there here not
reported here but from 700 kilometers up
to 10,000 kilometers we have EXO sphere
exosphere right now if you look at how
the temperature and the pressure changes
in the atmosphere as we go up here you
see again there is a change of
temperature fluctuations like this and
what we see here the boundaries between
those layers usually at the maximum
point or some change in the temperature
I should say temperature changes for
example up to here temperature decreases
decreases now from here it start
increasing at this change temperature
change actually and we have the end of
the troposphere or assume that that's
the boundary between those two layers
and here again you see another maximum
temperature change taking place in this
case then it start decreasing and then
comes over here then it start increasing
you see all these temperature changes in
fact we have the boundaries of the
layers in fact between the layers as a
matter of fact now let's look at what
the temperatures are and here you see
again we start from to 90 and that
corresponds about what 17 degrees on the
earth and then it goes almost to 215 210
this corresponds to about minus 60
degrees centigrade minus 60 degrees
centigrade now then when we go to the
stratosphere the temperature changes
increases a little bit but not much and
then up to this boundary again it almost
comes to 270 there and then from there
in the mesosphere and it goes in this
directions like this
and then this point here the temperature
is minus 85 somewhere about - if you
calculate that even that in fact - 80
here will be 100 and so on but what we
know that the average temperature in
mesosphere is about - 85 degrees
centigrade and it is reported to be the
coldest part of the earth in the
actually in the atmosphere coldest part
the average temperature is minus 85
degrees centigrade minus 85 degrees
centigrade now from this point on in the
thermosphere the temperatures start
increasing increases increases increases
it goes up to what up to 1500 degrees
centigrade 1500 but what does it mean
because that means it's very very hot
there no I will try to explain you in
the next hour okay