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Surface chemistry
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,1 There is no surface interface between due to complete miscibilitygases
or
.
2
Interface is few molecules thick ,
but its area depends Size
on of
particles in bulk phase
.
3
Adsorption The -
accumulation of molecular species at surface rather than in
the bulk of a solid or liquid is termed adsorption .
.
4
Adsorption in action : · If air in Closed vessel Containg powered Charcoal
will adsorb in its surface
dye soln
·
-
with animal charcoal
·
9. raw Sugar becomes colorless with animal charcoal
air becomes dry in Silica gel (adsorbs waters)
·
5.
5
Removing adsorbate from adsorbent surface is desorption .
.
6
water vapour is absorbed by anhyd Cac .
and adsorbed by Silica get
.
7
Sorption -
Adsorption + Absorption (Simultaneously)
, .
8 forces
Adsorption is due to unbalanced at surface
.
9 Adsorption Surface Pressure
depends on area
per unit mass , and temp .
10 &H of adsorption is
always negative
.
11 .
in Adsorption AS is also negative due to loss of freedom of movement .
12 AG AH-TAS both
DHEAS ve the AH Should be sufficiently
.
=
as are
-
more -
ve than AS to be spontaneous ·
13 less-re Dh
When Adsorption proceeds At will become An TDS 0
=
and So
.
=
which is
equilibrium State .
14
Adsorption
-
↓ ↓
Physisorption Chemisorption
·
weak Van der waan's forc Chemical
·
bonds (Kovalent or ionic)
·
needs Activation energy
D
·
Lack of specificity as VDW is
·
high specificing due to chemical
Universal bonds
gas with Critical temp irreversible
high temp
·
a
·
more .
,
are absorbed more than less
high pressure is favored
Critical gas . ·
more S A .
more adsorption
·
is reversible by heat due ·
Enthalpy of
adsorption -
180-240kmoil
to Le-chattier's principle An = -ve ·
unimolecular
layer
So
heating shifts left side - increases with low temp .
·
more surface are more adsorption
·
enthalpy of adsorption (20-40k]moi)
·
multimolecular layer
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