Scattering of light

Emulsion-Dispersed phase
Dispersion meduun -liquid

Adsorption leads to decrease in randomnes (entropy).i.e, ΔS < 0 for the adsorption to occur, ΔG slhould be -ve. We know that ΔG = ΔH - TΔS if ΔS is -ve, TΔS is +ve.It means that ΔG will become negative only when ΔH is -ve and ΔH > TΔS.

\(\frac{x}{m}\) = K.p^1/n
log \((\frac{x}{m})\) = log K + \(\frac{1}{n}\), log p
y = c + mx
m = 1/n and c = log K

The intermediate compound formation theory :
A catalyst acts by providing a new path with low energy of activation. In homogeneous catalysed reactions a catalyst may combine with one or more reactant to form an intermediate which reacts with other reactant or decompose to give products and the catalyst is regenerated.
Consider the reactions :
A+B➝AB; C is the catalyst .............(1)
A + C ➝ AC (intermediate) ..........(2)
AC + B ⟶ AB + C ...............(3)
Example 1:
The mechanism of Fridel crafts reaction is given below
\({ C }_{ 6 }{ H }_{ 6 }+{ { CH }_{ 3 }Cl\overset { anhydrous\\ { AlCl }_{ 3 } }{ \longrightarrow } }{ C }_{ 6 }{ H }_{ 5 }{ CH }_{ 3 }+HCl\) 
The action of catalyst is explained as follows
CH₃Cl + AlCl₃ ⟶ [CH₃]⁺ [AlCl₄]^-
It is an intermediate.
\({ C }_{ 6 }{ H }_{ 6 }+\left[ { CH }_{ 3 }^{ + } \right] \left[ { AlCl }_{ 4 } \right] ^{ - }\longrightarrow { C }_{ 6 }{ H }_{ 5 }{ CH }_{ 3 }+{ AlCl }_{ 3 }+Hcl\) 
Example 2:
\({ { 2KClO }_{ 3 }\overset {\\ { MnO }_{ 3 } }{ \longrightarrow } }{ 2KCl }+{ 3O }_{ 2 }\)
Thermal decomposition of KCIO₃ in the presence of MnO₂ proceeds as follows. Steps in the reaction
2KCIO₃ ⟶ 2KCI + 3O₂ Can be given as
2KClO₃ + 6MnO₂   →  6MnO₃ + 2KCl
It is an intermediate
6MnO₃ → 6MnO₂ + 3O₂
Example 3:
Formation of water due to the reaction of H₂ and O₂ in the presence of Cu can be given as
H₂ + 1/2O₂ → H₂O 
2Cu + \(\frac{1}{2}\)O₂   → Cu₂O
It is an intermediate.
Cu₂O + H₂  → H₂O + 2Cu
Advantages:
This theory describes
(a) The specificity of a catalyst and
(b) The increase in the rate of the reaction with increasc inthe concentration of a catalyst
Limitations:
(a) The intermediate compound theory fails to explain the action of catalytic poison and activators (promoters).
(b) This theory is unable to explain the mechanism of heterogeneous catalysed reactions.

(i) Emulsions are used in food industries. Food stuff like milk, cream, butter, etc., are emulsions.
(ii) Emulsions are very common in pharmaceutical industries. Many medicines are produced in the form of emulsions. Ex: Milk of magnesia is used for stomach troubles. Many lotions and ointments are emulsions.
(iii) Non ionic emulsions are most popular due to their low toxicity.
(iv) Cationic emulsions have anti microbial properties.
(v) In agriculture industry emulsions are used as delivery vehicles for insecticides, fungicides and pesticides.
(vi) In cosmetics, emulsions are the delivery vehicles for many hair and skin conditioning agents.
(v) The blood, protoplasm in plant and animal cells and fats in intestines are emulsions.

Factors affecting adsorption
Qualitatively, the extent of surface adsorption depends on
(i) Nature of adsorbent
(ii) Nature of adsorbate
(iii) Pressure
(iv) Concentration at a given temperature.
1. Surface area of adsorbent:
As the adsorption is a surface phenomenon it depends on the surface area of adsorbent. i.e., higher the surface area, higher is the amount adsorbed.
2. Nature of adsorbate:
The nature of adsorbate can influence the adsorption. Gases like SO₂, NH₃, HCl and CO₂ are easily liquefiable as have greater vander waal's force of attraction. On the other hand, permanent gases like H₂, N₂ and O₂ cannot be liquefied easily. These permanent gases are having low critical temperature and adsorbed slowly, while gases with high critical temperature are adsorbed readily.
3. Effect of temperature:
When temperature is raised chemisorption first increases and then decreases. whereas physisorption decreases with increases in temperature.
4. Effect of Pressure:
Chemical adsorption is fast with increase in pressure, it cannot alter the amount of adsorption. In physisorption, the extend of adsorption increases with increase in pressure.

S.No	Physical adsorption or vander waals adsorption or Physisorption	Chemical adsorption or Chemisorption or Activated adsorption
1.	It is instantaneous	It is very slow
2.	It is non-specific	It is very specific depends on nature of adsorbent and adsorbate
3.	In Physisorption, when pressure increases the amount of adsorption increases	Chemical adsorption is fast with increase pressure, it can not alter the amount.
4.	Physisorption decreases with increase in temerature	When temperature is raised chemisorption first increases and then decreases
5.	No transfer of electrons	Chemisorption involves transfer of electrons between the adsorbent and adsorbate
6.	Heat of adsorption is low in the order of 40kJ/ mole.	Heat of adsorption is high i.e., from 40- 400kJ/mole.
7.	Multilayer of the adsorbate is formed on the adsorbent.	Monolayer of the adsorbate is formed
8.	It occurs on all sides	Adsorption occurs at fixed sites called active centres. It depends on surface area
9	Activation energy is insignificant.	Chemisorption involves the formation of activated complex with appreciable activation energy.

S.no	Sol	Gel
(a)	The liquid state of collidal solution	The solid (or) semi solid stage of a colloidal solution.
(b)	Very low viscosity	Very high viscosity
(c)	It does not have definite structure.	It possesses definite structure.

By addition of suitable electrolytes precipitated particles can be brought into colloidal state. The process is termed as peptisation and the electrolyte added is called peptising or dispersing agent.
\(\underset { Precipitate }{ AgCl } \overset { HCl }{ \longrightarrow } \underset { Colloid }{ AgCl } \)

A minimum of 6.6 ml of AB is required to coagulated the sol.
The number of moles of AB in the sol is
= \(\cfrac { 6.6\times 0.1 }{ 20 } \) 
= 0.033 moles
This means that minimum of 0.033 moles or 33 millimoles are required to coagulate 1litre of sol.
∴ Flocculating value of AB for sol = 33.

The critical temperature of NH₃ is 406 K and that of CO₂ is 304 K. So, NH₃ has higher critical temperature and greater VanderWaal's forces of attraction than CO₂. So NH₃ will be more adsorbed than CO₂.

A sol is electrically neutral. Hence the medium carries an equal but opposite charge to that of dispersed particles. When sol particles are prevented from moving, under the influence of electric field the medium moves in a direction opposite to that of the sol particles. This movement of dispersion medium under the influence of electric potential is called electro osmosis.