Adsorption: Chemisorption & Physisorption (Part - 6) - Surface Chemistry, Chemistry, Class 12 Video Lecture

hello friends this video on surface
chemistry part 6 is brought you by exam
viacom no more fear from exam come you
see there are two type of adsorption one
is the physical adsorption right
physical adsorption the short curl it
fizzy Jobson is he short right so in
this case there is no chemical reaction
the example accumulation of dust
particles in the skin absorption of
hydrogen or chlorine gas by charcoal or
this water molecules adsorption on the
plastic the next is the chemical
adsorption right so if you see that will
called Kimi sorption also chemical came
over to the chemical comes kemi's option
good example is rusting of iron so here
actually chemical reaction takes place
on the surface so we will not discuss
these things in detail physical
adsorption and chemical option first is
physical adsorption that is
physisorption so in this case if you see
the accumulation of gas or small
particles on the surface of the
adsorbent occurs on the account of V
Vander Waal force we van der Waals force
example this dust particle sticks to the
skin because of equal work force the gas
molecules stick to the charcoal we go
under will force water molecules stick
the plastic will speak or reinforce or
this water molecules stick this leaves
because of V quarter one force
correct there is no chemical reaction
there is no
chemical reaction between adsorbent and
adsorbate
there is no chemical reaction because
I'm whisky there is no reaction between
the dust in the skin there is no
reaction in the gas and charcoal there
is no reaction in water and the plastic
there is no reaction in the water
hey since there is no chemical reactions
all week wonderful force here so Delta H
value is less actually and we have told
adsorption is always exothermic cross
and so it has to be negative but Delta H
is in the range of minus 40 kilo Joule
per mole it is less as compared to
chemical adsorption we'll see that right
there mildly you coming my liga coming
and generally they occur at low
temperature low temperature you see all
the reactions the sticking clear body
low temperature this experiment we
performed at low temperature generally
they happen at low temperature right so
here Wonderwall force is the one which
is responsible whatever force can be
either
I pulled able attraction London force
all the kind of course our resin was
responsible for physical adsorption then
the chemical adsorption or Kimmie's
option right so in this case what
happened the adsorbate our hand to
adsorbent by chemical bond so there is
something called adsorbent adsorbate and
we have something on adsorbent and they
are headed by a chemical bond for
example oxygen is my adsorbent and iron
is man sorbent
they are held by a chemical bond right
iron oxygen react and forms anything but
trusting of iron it's very known
equation and these chemical bonds can be
ionic or covalent since this involves
reaction and in this reaction if you see
any reaction this is a chart we have
seen is a barrier here so it involves
high energy back
so if you have any doubt on activation
energy can watch the previous chapter
video where we explain explain the
activation energy concept right it
involves high energy of activation since
it involves high energy of activation is
also called activated adsorption is also
called activated and sorption
because it involves high energy of
adsorption then this actually the
chemical reaction take place okay now
these two kind of adsorption which I
talked about physical adsorption
chemical adsorption actually they can
happen together also right it is not
necessary that only one type of
adsorption will happen so both can hop
happen whether also for example you see
this is hydrogen and nickel so when you
do hydrogenation of any substance we do
you use we use hydrogen and we use
nickel catalyst nickel plate like nickel
plate it provides the surface so here if
you see first the hydrogen is adsorbed
in nickel by the vulnerable force and
then hydrogen molecules dis is filled to
form hydrogen atoms correct and that is
my chemical absorption where hydrogen
molecules break into hydrogen atoms in
there stick to this nickel plate you see
this is my Hamilton atom this you you
are an emission for this the first one
if you see the metal adsorb hydrogen gas
correct so this is the mind what
physical adsorption this is my metal and
this is my hydrogen gas and this is and
so correct this is my physical
adsorption once again just hydrogen this
is my hydrogen hydrogen atom is adsorbed
by this metal is blue or is my nickel
metal this is my
this is not only physical at auction
took place now what happens if you see
these bond becomes weakened actually if
you see this this is a metal bond that
it becomes weaken metal comes near the
surface and this born and break now see
this bond and break this bond broke and
it forms what two hydrogen right 1 H 2
becomes 2 H so here if you see chemical
the auction took place now if you you
must have seen this in the hydrogenation
at Lee know these two it attached this
alkene and alkyne moves on is alkyne
became alkane and another set of alkyne
comes and again same thing happened
first hydrogen molecule gets adsorbed on
the Snickle physical absorption and it
breaks then two hydrogen chemical
adsorption and then again alkene comes
and it takes this 2 hydrogen in becomes
alkane mean another it comes this is how
it happens right so here and if you see
this is nothing but how nickel is acting
as a catalyst Hey so if using in
catalyst adsorption is playing a
critical role we'll discuss about these
in details when I talk about the
catalyst in the shotgun
correct so the point I'm trying here is
both physical and chemical adsorption
can happen together okay now we have
discussed physical and chemical
adsorption but we didn't discuss in
details let's understand some of the
features of the physical adsorption and
then we'll discuss the features of the
chemical adsorption right the first is
the lack of spicy cooking it is not
specific because the adsorbent doesn't
show any preference for a particular gas
if you use charcoal charcoal can absorb
hydrogen gas roaring gasp nitrogen gas
doesn't matter why because the
critical thing that is hair is won't
over force right and wonder what forces
universal it is universal so it is not
specific it because Honda water well
force is a driving thing here that is
running the show and whatever force is
universal so it is not specific example
char here this leaves can adsorb water
molecule leap in scarrans of milk also
please can also paint also it leaves can
absorb anything really your skin can
absorb water it can absorb some milk it
will draw does same thing this plastic
in adsorb cold rain you can resolve milk
it can absorb water it can absorb a lot
of things it cannot it's all okay the
second thing is it does depend on nature
absorber it does depend on nature of
adsorbate see amount of the gas or
liquid that is adsorbed by a given
adsorbent that depends on the nature of
adsorbent with gas or liquid so it would
take a easy liquefiable gas they can
easily be adsorbed for example if you
take 1 gram of charcoal read it charcoal
it'll absorb sulfur charcoal adsorb so2
more but we he dreads off less the same
ground charcoal will adsorb
so2 more sulfur dioxide so the nature of
adsorbate metals right so if it is
easily liquefiable gases or liquid it
can easily be ads on the next is
reversible leisure so these are
reversible physical adsorption is it is
a reversible you can just heat it and
you get it back example or they told
charcoal is used to store hydrogen gas
so you push higher up past hydrogen gas
through charcoal the charcoal surface
will adsorb hydrogen gas but the moment
you heat it up the hydrogen gases
Pretty's back right so physical
adsorption of a gas by a solid is
reversible correct so I can write it an
equilibrium reaction actually have ads
or wait you have ads or Bend that will
be in the equilibrium with the same
adsorb a plus and adsorb n plus M heater
so you pass something you get back this
right the next is surface area so as I
told adsorption is totally dependent on
surface area it is directly proportional
to surface area so that's why here was a
physical adsorption is a chemical
absorption both can be absorption
adsorption is slightly dependent on the
surface area and that's why we break the
metals or the adsorbent into small small
piece so that it can have more surface
area and it becomes a good adsorbent
right so we generally talk about the
fine
divided finely divided adsorbent why
because the finely divided adsorbent has
more surface area and more surface area
means for adsorption the next is
enthalpy of adsorption so enthalpy of
adsorption is low we have discussed this
in enthalpy of adsorption is low
normally 20 to 40 kilo Joule thermal
then this my mind lee exothermic my
links the right it occurs at very very
low temperature not very little bit
normally in low temperature right these
are the physical properties are features
or the physical adsorption the next is
chemical adsorption so let's see the
features of the chemical adsorption the
first is the highly specific C it occurs
only when there is a possibility of
chemical reaction between the adsorbent
and adsorbate
example gold will not absorb oxygen but
iron can adsorb oxygen because iron can
react with oxygen right similarly
hydrogen is adsorbed on metals because
hydro metal hydride came from so
hydrogen and normally if you see
hydrogen and oxygen can be absorbed by
reactive metals I'll say because they'll
form a metal oxides in metal hydride but
we would talk about the non reactive
metals like gold you do not react with
hydrogen it will not take the oxygen so
in that case
and as you see the iron rusting is more
prominent you never see gold getting
rusted correct so it happens only when
there is a possibility of chemical
reaction so it is specific it is
irreversible
obviously once i justed you cousin can't
get it back correct because see the
chemical reaction happened the new
compound got form so it is generally
irreversible correct
it is very very slow why very slow
because it involves high eclipsing
energy right it involves high
occasionally so it is very very slow
right because high activation there is a
high activation energy it is he talked
us at very high temperature since again
it has high activation energy needs a
little high temperature too for the
reaction you have a correct also a high
pressure and high temperature both
favors chemical adsorption you have seen
that in physical adsorption we are
looking for low temperature in this case
we are looking for high temperature and
high pressure surface again same in in
the physical adsorption also we need
more surface area and chemical
adsorption also we need more surface
area right so enthalpy of adoption as I
told it is high right it is very it is
high and Delta H is almost in the range
of 80 240 kilo Joule per mole why by
this why because inwards bond formation
and old bonds are broken you want
created so that Delta H is pretty high
so enthalpy of adsorption is also high
temperature also is quite very high and
it is little slope all these things are
linked actually correct
you know it is compare these good to
kind of adsorption this is physical
adsorption chemical adsorption in
physical adsorption the example I gave
is the water molecule is getting
absorbed by leaves and the chemical
adsorption a good example the roasting
of iron so physical adsorption it arise
because of the wonderful force chemical
adsorption arise because of chemical
bond formation it is not specific
physical absorption because the whatever
for should be versal it is highly
specific because
bond has to be formed chemical reaction
should take place so reversible in
nature
this is irreversible because it is a
bond formation it is mildly serving
and this is highly disturbing enthalpy
of adoption slow in that way of
adsorption is high low temperature is
good for physical adsorption high
temperature is good for physical
absorption in fact high pressure is also
good right so thus it decreases in
temperature because the low temperature
is favoring this adsorption it decreases
money is a temperature right and here
does other way around it it increases
with increase in temperature please note
these two are exactly same actually
these two points right since there is no
chemical bond formation so activation
energy is not required here a higher
activation energy required because the
new bonds are form both increases with
the increase in surface area and this
has multi molecular layer adsorption
this has uni molecular layer of
adsorption thank you visit exam viacom
to watch more videos Atem free online
tests get free study materials find
tutors and mentors and much more trying
salsa game