chemicals mmm
studies as a matter of
and we said that too
chemical reactions transformations of
those energies in one form to the others
and to what extent a chemical reaction
will proceed to the direction it's
written actually to the product and all
of these are so dynamic subjects and we
also simply define the internal energy
and enthalpy just refresh our memories
about those because we have covered
those in chapter 5 and the first law of
thermodynamics actually remember which
says that the total energy of the
universe is constant so you cannot
create energy out of nothing nor you can
destroy the present energy you can only
just transform one form of energy to
another form but the total energy of the
universe is constant that's the first
law of thermodynamics actually now the
both we said the enthalpy and the
entropy are state functions we also
refresh our memories about the state
function remember the change in state
functions only depends on the final and
initial state not the path followed from
the initial to the final state as we
said and both enthalpy and entropy are
state functions on the other side the
heat which is represented by Q and work
which is represented by W are also
thermodynamic terms tenet we use those
dynamics functions they are not state
functions that they're not state
functions and again we talked about
spent spontaneous process we define what
a spontaneous process is remember again
if a process is taking place by itself
without any outside assistance or
interference that process is called
spontaneous process spontaneous process
and we also simply talk about the
non-spontaneous process and the
reversible processes - but we just
indicated that the spontaneity of the
process is also affected by the
temperature of the surrounding
temperature of the system actually as we
have given example like mountain of ice
above zero is spontaneous but mountain
of ice below zero is not spontaneous is
not a spontaneous reaction it doesn't
take place by itself
now we're reversible and irreversible
processes again when we say reversible
process we just mentioned that we have
to remember the equilibrium processes in
thermodynamics literally means that if
you simply change one of the function
infinities will amount the process
should be reversed but infinitesimal
amount so for this only the equilibrium
state is appropriate and when we say
reversible process and thermodynamics we
mean that it is the equilibrium State
equilibrium State for example when we
talk about the mountain of ice and if we
talk about the reversible process
irreversible mountain of ice to the
water we mean we have to carry out at
the melting point of ice which is zero
degrees centigrade or 273 any other
temperatures the mountain of ice will
not be a reversible process but it will
be irreversible process we also said
that all spontaneous processes are
irreversible processes or spontaneous
processes are irreversible processes now
we try to define another state function
entropy again and entropy is a measure
of randomness of a system or you can say
it's MN on the
other side you can define it as the
measure of order now as the order of the
system increases entropy decreases as
the chaos increases entropy increases
again as the randomness increases
entropy increases randomness decreases
entropy decreases that means order means
low entropy and disorder chaos means
high entropy that's what we have to
always remember in terms of the entropy
and since the entropy is a state
function then the entropy change of a
process will be given as the initial
final entropy of the system minus the
initial entropy of the system this is
going to be Delta as again depending on
the sign of Delta as if it is positive
means there is an increase in the
entropy and if it is negative that means
there is a decrease in the entropy of
the system this is a gain for the system
yes how do we define order in chemistry
okay if you have let's say a pure
crystalline substance pure crystalline
at zero Kelvin it is the maximum order
right now if you increase the
temperature from there that take that
crystal increase now zero Kelvin
remember zero Kelvin that means every
vibrational rotational translational
motions stopped so we have an actually a
maximum order of the atoms or the
molecules or the ions in the crystal
that is the 100% water now when you have
100% order as we will talk about that
again few minutes later that means that
the entropy is what yes the entropy is
zero right if you have real order simply
entropy zero
then if you increase the temperature
then the molecule will start moving
around making vibrational rotational
motions and they can probably melt from
solid to the liquid again freedom of
movement increases and so on that means
the entropy increases okay so we that's
actually we have to think about the
motions of the molecules when we think
about the order in chemistry right
motions of tomorrow we will talk about
that more actually yes
so now again we can simply calculate the
entropy of change if you know the Q
reversible for that process that means
if you have the heat involved in a
reversible process we can calculate the
entropy change for that process must
just divide in the heat involved that is
the reversible process divided by the
temperature and this temperature has to
be constant again right that has to be
constant okay now second law of
thermodynamics remember first law is
about the energy of the universe which
says it's constant there were changes
this is the second law now the second
law of the universe again as we talk the
entropy of the universe in a spontaneous
process in any spontaneous process
increases as we said last time the
entropy and the internal energy behaves
differently in this case like the total
internal energy total energy of the
universe is constant right as we said in
the first law of thermodynamics but the
entropy of the universe is not constant
it always increases with spontaneous
processes when spontaneous processes are
taking place the entropy increases this
is the second law of thermodynamics what
it means again in equations that they
put it in the equation form Delta s
universe will simply be greater than
zero for spa for irreversible process
remember all irreversible processes are
spontaneous processes actually so that
spontaneous process the entropy of the
universe increases now what happens it
says if the process is reversible what
does that mean that means equilibrium in
that case the entropy of the universe is
not increasing it's equal to constant
value again now so remember again now
dropping this here it's a spontaneous
process that means that the entropy of
the universe increased certain amount
right now if I take this from here and
bring it up here what happens in the
entropy of the universe increase or
decrease hmm is this process spontaneous
no right so when it's not actually this
is not spontaneous but it's is it
reversible let's put it that way
is it reversible it's not spontaneous
but is it reversible no it is not
reversible
therefore again the entropy of the
universe is increased now to have a
reversible process dropping or taking it
out to make it reversible what should I
do it should probably take almost like
years and years to bring it from up here
to down there such that you know keep it
at equilibrium sort of like always in
equilibrium phase which is you know
that's again not possible to do that but
again both dropping taking it out are
irreversible processes and all
irreversible processes the entropy of
the universe increases irreversible
process and if the entropy of the
universe increases okay now entropy in
the molecular scale again like we talked
about last time when you have two
molecules containing this flask over
here and this flask is empty when we
open it up that means that this
molecules will move
to here actually if you have more
molecules and I will move all over fill
out the whole things and this is a
spontaneous process a spontaneous
process what does that means that means
that the entropy of the universe should
increase right and it does actually
because when you simply open this valve
here and let this molecules simply
diffuse or a fuse into this if this is
vacuum effusion over here then there
will be four possible distributions of
these two molecules in two flasks
right now the simply if you consider for
example any of the gas molecules blue or
red being in this flask in this class
the probability will be 2 over 4 that
means 1 over 2 or if you simply consider
two molecules being here again the
probability is 1 over 4 right 1 over 4
and so on so in other words the
probability of having two molecules in
the same flask is much less than
probability of having one molecule in
one class and the other one and the
others now consider you dealing with one
mole of gases how many molecules of gas
we have am pagano's number of molecules
and remember the Avogadro's number is
very very large number 602 times 10 to
the minus 10 to the 23 that's a big
number it's actually bigger than we can
imagine
we can simply and in that case if you
have one mole then the probability of
having one distribution or having all
gas molecules being in the same flask
will be 1 over 2 power to the Avogadro's
number that is 1 over 2 power 2 to the
10 to the 23 something like that what
does that means
there will be very very large number of
different ways of distributing actually
one mole of gas into two flats and the
probability of having all gases in one
flask will be very close to zero it will
be like 1 over infinite almost right so
that means that the molecules when you
let this flat simply open this switch
here and let them go here they will
never be back again both here as a
matter of fact especially if you're
dealing with large number of molecules
large number of molecules and again the
entropy of the system will be related to
the number of different distributions of
these molecules into this glass air 2
flask again and simply in this case like
when you have this over here there's
only one way to submit in that there's
two of those in the same flat
but when you open the valve here and let
the two these two molecules expand and
there will be four distributions
and if you have more there will be more
distributions and more distributions and
more distributions depending on the
number of molecules that means more
distributions means that the entropy of
the system is increasing the entropy of
the system is increasing because having
one distribution in fact probability of
heaven one distribution would be 1 over
that very large number and that number
goes to infinity and the probability of
heaven that particular arrangement will
be close to zero actually right close to
zero now the question here is how can we
relate the entropy to the molecules at
the molecular level molecular motions
the system now remember again the
thermodynamics particularly looks at the
ball properties it said like we have a
substances it's a big picture you know
we for example you just take this here
this pointer and if you take consider
this whole things that's the bulk things
right and it's hard it's a both
properties and other things the
temperature and so on but if you go to
the molecular level an atomic level that
means we start thinking about what is
this made of
what atoms carbon hydrogen oxygen maybe
some other elements and so on that is
the again the molecular atomic level
what is this structure is this a
crystalline type structure or a
different type structure what is the fit
is crystalline what is the unit cells
and so on so all of these are molecular
level properties molecular level
properties so can we relate the entropy
to the molecular level properties of the
substances actually now how do they
relate that means how the molecular
scale molecular properties molecular
motions relate to the entropy now for
this we use it says statistical
statistics and that's called the
probability statistical thermodynamics
usually this is called statistical
thermodynamics and again in statistics
we mostly talk about the probability
right the field is called the
statistical thermodynamics and then we
simply talk about microstates a single
possible around rate of positions and
kinetic energy of the molecules now
let's see what this is what this simply
means again but let's look at what we
actually the answer how the entropy is
related to the atomic level properties
atoms molecules and so on is given by
Boltzmann here and
horsemen define the microstates many
possible micro days we can look at every
pic there are picture W represents the
number of microstates entropy is a
measure of how many micro cells are
associated with a particular microscopic
state with macroscopic States now the
connection between the number of
microstates and the entropy of the
system by Boltzmann actually given as
this entropy office system of whatever
you're talking about would be equal to K
which is constant it's called the
Boltzmann constant the value of that is
actually R over Avogadro's number the
gas constant divided by Avogadro's
number and natural logarithm of W now W
is the number of micro State number of
microstate
what is a microstate I guess we have to
define what a microstate is now let's
assume that we simply have one mole of
gas in a container one mole of gas at a
pressure temperature some temperature
and pressure yeah how many molecules 602
times 10 to the 23 molecules huge number
of molecules now these molecules are
simply moving in their space in all
directions there are collisions between
them and also every molecule has a
kinetic energy right and the
distributions of the kinetic energy
remember with the temperature we simply
have molecules with very low kinetic
energy and then the molecules which have
the average kinetic energy and then the
Maalik
which have very large kinetic energies
right so they are all moving and we know
that as the temperature increases the
kinetic energy of the molecule increases
this is how the energy is simply stored
in the system by increase in the
temperature we store there more energy
and the kinetic energy of the molecules
increases now suppose that we have a
camera which can take a snapshot and an
instant time there were short time and
sees the molecule right so let's say in
an instant time just just this is a
picture just a picture of all of the
molecules there then I will simply have
a distributions that say like this now
remember all of these are molecules and
they have different plays let's assume
that this is one picture a snapshot but
now not only the places but suppose that
this camera also measures the kinetic
energy of every molecule right kinetic
energy of every molecule so we have the
kinetic energies actually and directions
and kinetic energies that means 1 over 2
MV squared on every molecule but the
kinetic energy of the molecules will be
different again all different now this
actually if I can simply take a snapshot
stop the system and determine the
positions of the molecule and also their
kinetic energies this will be a
microstate right a microstate now so the
microstate actually microstate actually
tells you that just one of the
distributions of the molecules in the
space
with their positions and also the
distributions of the kinetic energy to
the molecules right now suppose that
another instant time you take another
snapshot right and in that snapshot
let's say you have simply another
snapshot here and you have again the
molecules like this remember this is
Avogadro's number if you're talking
about one mole of gas now in this case
every of those atoms are at different
place plus their kinetic energies may be
different because the collusions and so
on right may take place so this will
simply give you another distribution of
the molecules with their positions and
their kinetic energies this is going to
be another microstate right now then I
can take the third forward thought how
many of those can I find it out hmm very
not easy
that's what Boltzmann did actually the
Boltzmann was able to calculate the
number of microstates of
a system and a given temperatures and
pressure and he find out this this value
here right here this W so that W is
actually the number of microstates that
means how many different ways the
molecules can be distributed in space
and with the kinetic energies all of
those have different kinetic energies
right so and that is W that means that
the larger the number of microstates the
larger will be entropy of the system so
the randomness actually will increase
with the number of microstates and this
can be calculated this can be calculated
but think about again
is positional distributions and the
kinetic energy distributions of the
molecules at different times you know
there's so many but that is that can be
calculated and it's equal to the W
Boltzmann said and he said that if I
simply take the logarithm of that
multiplied by the K constant volts my
constant this is called the Boltzmann
constant actually okay
and you get the entropy of the system
entropy Office's you see remember when
we talked about the enthalpy of the
system we said that we can't really
measure or calculate the absolute
entropy enthalpy of a system we can't
measure the internal energy absolute
total internal energy off the system too
complicated but what we can really
measure we said there we can measure the
change in enthalpy which is Delta H and
we can also measure the change in
internal energy which is Delta e right
capital e but in this case you see we
can actually calculate measure the
entropy of a system absolute entropy of
a system this is not change this is the
entropy of the system right now what you
should remember when we talk about macro
macroscopic scale that means macroscopic
state which is defined by a temperature
pressure a number of moles volume
whatever those things are for the gases
and this macroscopic state consists of
large number of microstates actually
right so every macro macroscopic state
corresponds to large number of
microstates there are a lot of
microstates like a gas in a container
one liter gas like this you can have
this distributions of kinetic energy at
position this one that one that one that
huge number of those and that can be
calculated that's equal to W okay now
again since the entropy is a state
function the final value minus the
initial value will give the overall
change
in this case an increase in the number
of micro state results in positive
entropy change and that is simply means
that increasing this is important
increase in the number of microstates
means higher entropy right higher
entropy and if we calculate the entropy
change for from initial to the final
case then we that will be equals to the
entropy of the final system system in
the final state this is the entropy of
the system initial state and this will
be equal to the debt entropy change
going from initial to the final state
again based on the number of microstates
that the system has right the number of
microstates now let's look at how the
volume and temperature change on the
system affects the entropy we can follow
it again if you increase the volume
there are more positions possible for
the molecules this results in more
microstates so increased entropy that
means if I put that 1 mole of gas not in
this container let's say this is like 24
liters suppose that I put it in 30
liters what does that means I will have
more space more space means that there
will be more possible microstates
actually for the system and increase in
the number of microstates means that the
entropy will increase so if you increase
the volume of a gas entropy increases
right increases now if you increase the
temperature the average kinetic energy
increases and also the the broadness of
the kinetic energy of the molecule
increases to remember the increase in
the temperature the shape of the kinetic
energy distributions like this and what
does that mean that means again that the
possible number of microstates that
means the molecules have been different
kinetic energies will increase and that
will also increase the entropy of the
system so average kinetic energy
increase this result in greater
tribunal of molecular speeds that's
important
that means more microstates right more
microstates and therefore there are more
possible kinetic energy values resulted
in more microstates increase in entropy
what does that means increasing the
temperature of gas will always increases
the entropy of the system entropy of the
system now how about the if I increase
the number of moles of gas
instead of like one mole if I put here
one point two moles of gas how that will
affect the entropy of the system
increased definitely if you increase the
number of particles molecules than you
increase the number of microstates
definitely and that will increase the
entropy of the system again now the
energy is simply stored in the molecules
in three different ways right I should
say form one is the translational energy
of the molecules and these are simply
due to the motions of the molecules this
is actually the kinetic energy movement
of the entire molecule from one place in
other this is a translational energy and
it's corresponds to the kinetic energy
now the vibrational energy and that is
periodic motions of the atoms within a
molecule that means at a certain
temperature if you have molecules made
of two atoms for example then these two
atoms makes this kind of motions and
this is called vibrational motion and
this vibrational motion corresponds to
an energy so the energy is stored in the
form of translational energy or in the
form of vibrational energy now if you
have simply molecules made of three
atoms then the number of different
vibrational energies or vibrational
motions will be more than the two atom
or die molecular species so
again as the number of atom increases in
the molecule then we rotate the
vibrational energy that stored there
also increases to now rotational energy
that means corresponds to the rotation
of the molecule around an axis which
axes this may be an X Y or z axis so
there are three different forms of
rotational energy - so on so again here
it says more atoms means more
microstates more possible molecular
motions again means higher entropy
higher entropy right so here the example
this is the water molecule these three
are vibrational motions again this for
example corresponds that at the same
time these two atoms are getting away
from each other and also moving to each
other closer away closer away and so on
and this does the same kind of things
you know up and down both of those now
this is again this angle changes opens
up and closes opens closes periodically
actually and this one is another
vibration motions this is called the
symmetric vibration motion this is
anti-symmetric that means as this atom
simply moves in this direction that
atoms goes in there as this atom goes
out this item goes out in that is
unsymmetrical vibration motions so all
of these kind of motions stores the
energies there right energies there now
entropy on a molecular scale again the
number of microstates therefore and the
entropy tend to increase with increase
in this is again sort of the result
conclusion with temperature increase in
volume increase in the number of
independent moving particles if you
consider the gas increase in the
temperature increase in the volume
increase in the number of moles of gas
always increases the number of
microstates increase in number of
microstates means increase in the
entropy you see again the end
Trippi of the system is determined by
the number of microstates that are
present in that system right number of
microstates now and how the entropy and
the physical states are related you can
easily guess this again entropy
increases with the freedom of the
motions of the molecules certainly if
they move more freely and for example if
you go from gas to the liquid to the
solid suppose that you have one mole of
gas water and then one mole of liquid
water and one mole of solid water if I
ask you which one will have the highest
entropy definitely the gas right and
then next one is we simply liquid and
the other one is the solid so this is
again yeah because the freedom of
motions of the molecules is largest in
the gas then less in the liquid and very
confined in the solid actually in the
solid we only have vibrational rather
than with translational no translation
only vibrational and rotational only
actually or even no rotational but in
the liquid we have simply translational
rotational and vibrational all of those
are there as a matter of fact so the
entropy decreases going from gas state
to the solid and increases going from
solid to the gas gas liquid and so on
entropy increases for four processes
where the gas formed from either solids
or liquids that means this is the first
one it says simply if a chemical
reaction or in a process gas forms from
the solids or liquids the entropy
increases right entropy will increase
liquids or solution form from solids
this is simply means that the mountain
of the solids and
that entropy again increases as the
number of gas molecule increases during
a chemical reaction if you dealing with
the chemical reaction entropy is also
increasing for example here is the
chemical reaction example nitrogen
monoxide reacting with the oxygen to
form nitrogen dioxide right so in this
reaction will the entropy of the system
will increase or decrease we will look
at the number of gas molecules number of
gas molecules so we have simply three
gas molecules in the reactant side and
we have two gas molecules on the product
side what does that means that means
three gas molecules our reactant to form
two gas molecules means the number of
gas molecules decreasing means the
entropy decreases so Delta s actually
for this reaction will be negative means
that the entropy of the system decreases
as a matter of fact so qualitatively we
can easily guess whether the entropy in
a process or a chemical reaction
decreases or increases as a matter of
fact now here that's the point here is
again we said the entropy particularly
off a system increases with increase in
temperature increase in volume if it's a
gas and so on now what happens if you
decrease the temperature entropy
decreases why because the translational
motion kinetic energy of the molecule
decreases because the vibrational
motions are decreases rotational
everything is decreasing as ATP so how
far we can go down we can go to zero
Kelvin right now when you go to the zero
Kelvin then every motions will stop
right those motions will turn off no
translational no vibration no rotations
now if you also have a solid with a
perfect structure pure compound solid
crystalline structure right no
impurities that point at zero Kelvin no
motions perfect order
means the entropy is zero right so this
is the third law of thermodynamics
thermodynamics simply says that at zero
Kelvin for pure crystalline perfect
crystalline substances the entropy is
zero entropy is zero now then if you
increase the temperature the entropy
will increase can we calculate that yes
we can calculate that if you simply know
the heat capacity of the substance at
different temperatures and we know at
melting and boiling it simply Delta H
fusion and Delta H vaporization we can
calculate the entropy of a substance or
a compound whatever
in fact at a temperature somewhere at a
temperature for example suppose that we
simply have hydrogen gas right and the
hydrogen gas let's say at 25 degree
centigrade if this is hydrogen gas it's
not actually but it will be equal to
this value here right not now aver these
will be calculated now you see again as
the temperature increases this is the
solids at 0 Kelvin right and temperature
increases the entropy will increase
increase increase due to what do to the
vibrational motions rotational motions
actually and translational actually not
in the solid but v2 the vibrational
action now when you get to the mountain
point here right
without the temperature increase we give
heat to the system and then melt it up
to here so at this point here all of the
solid that pure crystal there is liquid
right so the entropy is that much there
and then we increase the temperature of
the liquids and then here it is the
boiling point here right it all
vaporizes right temperature the same
temperature and the entropy increases
and then we go here and so on what does
that mean that simply means that if I
know that
data enough data and we do have the data
I can calculate the entropy of any
system at certain temperatures right at
certain temperatures and that entropy is
simply called the standard entropy of
the system again standard entropy of the
system and here are the standard entropy
of the hydrogen nitrogen oxygen gas
these are the things again sodium and so
on you see again the hydrogen gas this
is again joules per mole per Kelvin this
means for one mole of hydrogen again at
25 degrees Kelvin no 25 degree
centigrade 298 Kelvin is equals to 130
point 6 joules per Kelvin that is the
entropy of one mole of hydrogen now when
you go to the nitrogen again you see
it's little greater right 191 because we
are dealing with larger atoms nitrogen
is larger than hydrogen and the oxygen
and then goes to water and ammonia and
so on so these are the standard
entropies of the substances at 298
Kelvin or 25 Kelvin
now these are again called standard
molar enthalpy for gases are generally
greater than the liquids and solids
enthalpy yes now says be careful about
the size here and the standard entropy
increases with molar mass again that
means the bigger the molecule the larger
it is standard entropy but not that much
actually you see again it changes from
what hundred and thirty or let's say
what is the lowest one here the lowest
one is about what 72 even this is the
solid and the largest one is probably
about what 192 or this one 205 so that's
not that much actually
I mean not like 10 or 20 times like less
than two times but these are the
standard entropies what are they're good
for they're good for calculating
standard entropy change for a chemical
reaction right chemical reaction now
remember again to calculate the enthalpy
change of a chemical reaction we use the
standard enthalpies of formations right
standard enthalpies of formation now
remember in those cases the in turn end
up your formation was actually the
enthalpy change of a reaction in which a
substance is formed from its pure
elements understand standard state
conditions right so actually the
enthalpy of formation corresponds to the
formations of that substance from its
pure elements under standard conditions
and therefore the standard enthalpy of
formation for pure elements at their
standard states is assumed to be what
standard enthalpy of formation for pure
substance at standard state zero how
about here is the standard entropies are
zero
no it is not for pure elements actually
as you see over here for example
standard entropy of hydrogen is 130
nitrogen oxygen all of these standard
enthalpies of formations for all these
are zero right but for the standard
entropy they are not zero now let's look
at here again now there is an error here
let's see can you find that error now
here how we indicate the standard
entropy right
only s to the not right zero here now
here that will not be there right it
will not be Delta this is also will not
be Delta V R but this is Delta the
entropy change in a chemical reactions
right some of the standard entropies of
the product that Delta s zero does not
stand for standard entropy because here
here is the exact I mean look at this
this table here this is the correct form
of standard entropy as to the zero and
but again remember that that's not going
to be there that Delta and that Delta -
but it once you know the standard
entropies of the reactants and the
products you can calculate the entropy
change standard entropy change for the
chemical reaction using this formula
right using this formula well now again
N and M are the coefficients in the
balance chemical equations coefficients
in the balance chemical equations now
how about the entropy changes in the
surroundings yes we can simply calculate
the entropy change of the surrounding
heat that flows into or out of the
system changes the entropy of the
Saranda right now for an isothermal
process isothermal means constant
temperature process temperature process
the Delta s surrounding would be equal
to minus Q system divided by that
temperature now what does that means now
suppose that the two for the system is
negative right what is negative means
exothermic what does that mean that
means the system releases heat
to diss around it right so in that case
if Q is negative another negative here
divided by T Delta s Tirana will be
positive very clear actually when the
heat is given to the surrounding the
entropy of the surrounding increases
right that's positive but if we see the
the system observes heat from the
surrounding then the heat content of the
surrounding will decrease and that
decrease means that entropy of the
surrounding result also decrease so that
sign is actually important now at
constant pressure Q system is simply
equals to Delta H for the system again a
constant pressure remember under
constant pressure Q system is equal to
the enthalpy change Delta H so Delta s
surrounding would be equal to minus
Delta H system just that replaced by
Delta H actually divided by T at
constant pressure again now if I simply
have the Delta s universe and it would
be equal to Delta s system plus Delta s
surroundings for spontaneous process
Delta s universe will be greater than
zero this is a game the second law of
thermodynamics for spontaneous process
the Delta s universe will be greater
than zero and total entropy and the
spontaneity how the entropy and the
spontaneity are related again Delta s
universe is equal to Delta s system plus
Delta s surroundings yes now when we
substitute the Delta s surrounding with
Delta s system divided by T which we
have simply defined before and Delta s
universe will be equal to Delta s system
minus Delta H system and T all right now
if I multiply both sides of this
equation by minus T over here like this
and I get simply minus T Delta s
universe and minus T Delta s system and
Delta H system that goes
there now for the process to be
spontaneous
I guess rearrange that simply put that
over here and this there and I have this
equation here minus T Delta s universe
equals to Delta H system minus T Delta s
system now let's see what we have here
actually just go here for a spontaneous
process since Delta s universe will be
what spontaneous process Delta s
universe will be what is the sign
positive or negative positive it will be
positive increasing so multiplying that
minus T that means this will be negative
right so what does that mean if this
term is negative for a process minus T
Delta as negative for the process that
process is spontaneous right now how can
I calculate that if I know that Delta s
universe and minus T Delta s yes I can
do that but it would be very difficult
to calculate this Delta s universe here
but if I know the Delta EIJ system that
means the enthalpy change of the system
and if I know the entropy change of the
system remember I can calculate this
entropy change from the standard entropy
s if this is chemical reactions right so
that means if I know the temperature by
using these thermodynamic values I can
find out whether the reaction is
spontaneous or non-spontaneous or any
process will be spontaneous or
non-spontaneous so now this two is
combined with a new function
thermodynamic function which is called
Gibbs free energy and it is designated
by G capital G and simply the change in
Gibbs free energy would be equals to
this right here minus T Delta s universe
and that's equal to Delta H T Delta s
now all of these values are actually for
the system Delta s system Delta H system
and Delta G system all of those are now
system let me
if I know the enthalpy change of the
system and the entropy change of the
system at a given temperature I can find
out the Delta G Y because by looking at
the sign of the Delta G I can tell
whether the reaction is spontaneous or
the process is spontaneous or it is not
spontaneous if now the G chips free
energy change in the Gibbs free energy
turns out to be negative means that the
reaction or the process is spontaneous
if it changes to be it comes out as
positive means that that reaction or
that process will not be spontaneous but
the reverse will be spontaneous okay I
guess we'll have to stop here and then
next time we will continue