Bond, Lattice enthalpy - Thermodynamics Video Lecture - Class 11

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before watching the video please make
sure that you have watched part 1 to
part 19 bond enthalpy now we already
know that the energy is required to
break a bond and energy relays when the
world is far right and with respect the
chemical reaction they have two types of
terms we use one is the bond
dissociation enthalpy and the mean bond
enthalpy we'll talk about all these
things let's talk about the first part
bond this enthalpy so for diatomic
molecule for example hydrogen chlorine
oxygen you break the this is a molecule
only atom this guy is atom molecule two
atoms there is an energy released you
break it you need some energy actually
into energy that is nothing but the bond
is social enthalpy but in some case
example in polyatomic molecules ch4 if
you break the ch4 molecule form these
atoms covering four hydrogen atoms you
see that the first one becomes CH 3 plus
h 1 hydrogen out and then from CH 3 you
get CH 2 in vibration then from CH 2 you
get CH and 3 hi person and from CH you
get CN forever
see all these equation the Delta H is
not saying the Delta S will be X Y is
they all are different actually so this
needs less energy this needs more energy
all the more all the more so what we do
is we find the mean of that the total is
let's suppose this value and you want to
find the mean what enthalpy you divide
this by 4 because there are 4 bonds here
so whatever you get here for this is the
mean bond enthalpy example is the
methane molecule right you want to bring
the free
the first part you need less energy to
break the second one here in volume and
she heard burned all the more fourth one
all the burn rates it's quite so in that
case you are mean of all the energy
required and then you divide by this is
what again does mean warning that right
bond isn't always jellies for diatomic
molecules where there are the same
actually the same little molecules mean
little frequently one bond so the
valence there is no question of taking
me in his opponent and molecule here
take me you have this term con mean one
time they said because lattice in County
also so bonding that be I told as
something you know we have let suppose
water talked about gone between these
two light hydrogen oxygen is lattice is
something or ionic compound and they
told that everyone the molecules atom
they want to reduce the energy and it is
found that in the lattice form the
energy is less so for example sodium
chloride divine law is form this lattice
structure while the energy is less and
the model please energy they'll form
this lattice structure so then I see
less in the lattice structure if you
want to take out the atoms from this
lattice you have to provide some energy
right and that intervenes lattice
enthalpy is nothing but the enthalpy
change required and one more appealing
compound is removed from this lattice to
gaseous state you take out this and
curtains and in fine distance you take
out its green one big one in distance
that does nothing but my lattice
enthalpy right because
form length is mean in MX energy why
because the lightness is a steam esteem
stable state it has less energy the
lattice publish this thing you spread in
the last chapter we don't understand as
you can was last chapter we do where you
explain the these things change of
backbiting
so the example was I have this NaCl in
flatus form you want to break the sodium
chlorine in ions the gaseous form you
have to give this much energy 788 kilo
Judah alone but the trick here it's
impossible remind this lattice enthalpy
directly by expected so what we do is we
use a direct way and we use something
called born here a cycle to find this
lattice enthalpy because it's always
impossible to it experimentally break
this NaCl into any preferences melts I
notified the energy requires arms
Impossibles we used born-haber cycle and
that's not an auntie per cycle
let's do for sodium chloride see for as
the challenge here is was to get NaCl to
any plus plus so you start with this
this place the first thing we'll do is
we have this n is solid and I have my
curing gas the first thing that is
required as the sublimation of sodium we
want to convert this into gas steel so
what we need is sublimation of
sublimation enthalpy of sodium so from
solid and become gas so I have sodium
and chlorine burn gas now I have to
ionize this guy I have to be I have to
make it an a-plus so I need some
ionization in help you to make any plus
any gas will become any plus here and I
Eve enthalpy ionization for that so I
have any plus but I have my chlorine in
molecular form I have to make into atom
home not right so I will dissociate
I'll break the bond of chlorine to make
it glowing atoms so 1/2 C LT will become
C L so the bond is
so I have sodium ion and a chlorine gas
Radovic it sealed - so what I do is I
take out an electron from or put one
electron to chlorine electron gained by
killing so this becomes CL - from CN it
becomes CL - now I am na plus MGL - now
I am at a place and Cl minus then
immediately the lattice thing will come
and it will form an ECM so the lattice
energy is and entered are doing I am
forming an ECM correct and I also know
how to form any co directly so I don't
know this value but I know all these
values so I know you you reach from here
to here you get you have to spend a year
- you get four 11.2 laser energy or you
reach from here to here to here this is
awesome like she reach from here to here
to say you reach from here to there see
so this - 4 1 1 2 is nothing but 1 0 2
plus 4 9 5 6 plus 1 2 R plus minus 3 4 8
6 plus this X then this VX both are
equal that we can get that otherwise
correct that's what you want right
any CN 2 any plus say - so we will get
the value let me do it man singing they
start with here with this step now the
sodium will make sure EMS
so given gas i have sodium gas all I
know is this independent class I have
sodium plus na but I have terrine in the
molecule form and we get to Adam forth
now I had to make it CL - so L give an
electron way you make it CL - no I have
any person skill - both I want to make
it any CN so the lattice thing comes
here right because I told the lattice is
nothing but you have NaCl you break it -
concealment sign or you have any blossom
zeal - Han you bring them together it
will release energy to form an SEL
lattice so here we have an A+ in seal -
air release energy but what how much
energy is released we don't know we are
not able to calculate that just keep it
like that only will but but this is easy
to find we have we can get any CN
directly by using this reaction and a
solid plus Hacienda gas you can get the
enthalpy of formation of this NECN so
from this will begin to find them that
isn't wh right because this value minus
this value if you see - 4 1 1 2 so 1
point West
- 4 1 1 point 2 this will be equal to
this whole chain because from here you
reach you're using same please NaCl
either you go from this path this path
all same right we do saw a state
function so this is path 1 enthalpy the
part will have will also be saved apart
in w1 u1 0 8.4 plus mu 95 for you 6 +
120 1 plus -3 48 right 6 plus X both are
equal if you equate you will hit the
value of x that will be the pivot the
lattice enthalpy options you can take up
example so I can actually find Li e F so
here also li plus net minus sign in I
wanted to find the same thing the
lattice thing for Li air so ahead all so
you have this lithium salt and chlorine
gas you react you can easily find this
value this you can find you an
experiment or you draw in the next
approach you have this lithium solid you
make it a little gas you calculate the
enthalpy and
then you have obligation then you have
gas or gas using LA to LA plus you find
the enthalpy of ionization then you have
this morning gasps you make it to
molecule you find the enthalpy here
right the morning that it was all
swollen bonds are broken now you have
the spearing gas I have to make it f-
you measure this electron get enthalpy
and then this is something which is X we
don't move and then you you have these
values you have these values and
integral of X thank you
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