Adsorption Theory of Heterogeneous Catalysis Video Lecture | Chemistry Class 12 - NEET

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about various theories for adsorption
right that so can happens and we have
seen adsorption it depends on these
factors and this is something a national
phenomena to explain this national
phenomenon there or theories right about
the heterogeneous catalysis because
because you've seen this in the case of
heterogeneous catalysis adsorption plays
a major role correct now there are
various theories are to explain this is
the first were the adsorption theory for
heterogeneous catalysis the second is
the modern adsorption Theory third is
the energy activation Theory the porters
intermediate compound formation theory
so we will talk to these first two
theories only the last two unit will not
discussed in this chapter the first
theory is the adsorption board children
right so as for these three what happens
is the reactants are adsorbed on the
surface of the catalyst that's all these
reactants are adsorbed on the surface of
the catalyst and what happens in this
surface this is my catalyst on this
catalyst would embody icons are there
with this high concentration of reactant
see it is telling that the only thing
happens is my reactants they are
adsorbed on catalyst surface so as per
this old you only want this thing
happened and with this since that
suppose they are more and more reactants
here their word more way I can tell
right now it works like a platform it it
is a platform where we have more and
more reactants this the blue one is my
catalyst in the black area
right since more and more reactants are
on the surface the concentration of
reactants
on surface
of catalyst is more since the
concentration is of the reactant is more
reaction is faster right so as per the
old theory what happens is this
reactants gets adsorbed because the
adsorption concept was there so
according to old theory the reaction
tends gets adsorbed on the surface
since lot of reactant gets adsorbed on
the surface the concentration of
reactant or the surfaces more since the
concentration of the reactant is more in
the surface is more reaction in this
surface right the react form product
once the product is formed they all go
come on a new set of reaction comes so
that and does you see the catalyst was
not amused late it was when you get
almost same catalyst what it was but
this theory was ok convincing but it
could not explain one thing see
experimentally it is seen that if you
have you pass a big catalyst it supposes
big block of nickel right for a reaction
out of the reaction is over the the gram
eligible I have given hundred round
ickle I still get hundred gram of nickel
but a nickel now is in the port form
instead of big glob it is in the pollen
form that is what it has seen experiment
li so it is still hard gram this is
initial she's fine
and this is my catalyst this theory
could explain why the nickel is still
hundred gram but it did not explain why
this got finally divided into whatever
so for this a new theory came called
modern theory so to explain why the
catalyst is observed after the reaction
is finally divided this modern theory
came this series add-on on the old
theory she asked her old theory what
happens the reactants are adsorbed on
the surface of the catalyst that's up
right so in this case what is happening
is it says that two things happen the
first thing is
reactants adsorb on catalyst surface and
the second thing that happens is it
forms activated complex
and this activated complex is unstable
so you see this is my nickel or platinum
is my catalyst on this surface of this
catalyst this my reactant is my hydrogen
here hydrogen with many reactants will
get adsorbed was it is adsorbed now if
you see my other reactant came and it
forms an activated complex this is
active in complex and this is very
unstable this activated complex is
unstable and that's why hitting Freeth
rate of reaction now this unstable
active complex forms a new molecule so
this will form a new molecule where this
bond will break and these these bonds
will also break because now there is a
bond between hydrogen and nickel right
this morning breaking this bond and
break and this alkane will leave the
surface and again will create space for
new alkane alkene or new already gone
reactant to comes here we are taking a
reaction of alkene to alkyne
hydrogenation so new alkene will come in
a covalent surface and again the same
thing will happen in activated complex
could be form and that will be unstable
it will form alkene until you leave the
surface same thing will happen right so
this is nothing but it is an addition of
the old Theory inventory we say that
only the reactants or on the catalyst
surface in the concentration of reactant
is more in the catalyst up in the
reaction is faster in this case we're
talking about activated complex are also
right so now if you talk about the steps
in this there are five steps as
discussed the first step is diffusion of
reactants to surface of catalyst we have
seen there is equal adsorption right so
the first one is let me write this
diffusion of reactants to surface of
so once it is near the surface of
catalyst the second thing happen is
adsorption adduction of reactant to
surface of catalyst ocean of reactant to
surface of catalyst this is the second
step the third we have seen the
intermediate was formed so it is
intermediate formation it is a complex
intermediate formation or complex
unstable intermediate formation right
the fourth step is once in this form you
get the product right
the intermediate formation in the
product formation I can say it is all
saying because it is very fast it is
very unstable
once this is done these option happen
that is the desorption of the final
product and with this this goes off and
it creates space for the next reaction
and when this is done my the diffusion
of product away from catalyst diffusion
of luck are we this product will go away
see first thing is this reactant comes
near to the surface that is first assist
the second till the reactants are
adsorbed in the surface the third is
intermediate this form and the product
is also formed at that time the fourth
is desorption eighth the product is
detached from the surface the fifth is
diffusion of the product backed away
from the canister so this explains a lot
of thing first thing is it explains why
the mass of the reactor catalyst is not
changed you see the nickel is not used I
admit this is just providing a surface
to form complex intermediate but it is
not be consumed so it explains why the
mass of chemical mass and the chemical
composition of this
nickel is not change it also explained
by a small quantity of catalyst is also
a because event is small only of
catalyst the reactant comes they are
used up and now again the reactant or
the product goes back right into so the
just the surface area of the nickel is
useful to other reactant so it's like
even if there is small amount of nickel
it makes a huge difference right it is
not it this more amount of nickel is
usually for 10 or 20 molecules of
reactant the reactant use nickel for a
small amount of time and then it becomes
product and it lead the surface so the
same service is now being used by other
reactant so a small amount of catalyst
also makes a huge difference
right it also explains why powdered
catalyst is more effective because you
powder it you heat the surface idiot
here it's all about the surface area
right the motor surface area more is the
reaction but it could not explain the
action of promoters and poisons we have
seen the catalytic promoters and
catalytic poisons so it could not
explain this theory could not explain
promoters and poisons in guide list
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