Surface Chemistry MCQ Questions & Answers in Physical Chemistry | Chemistry

For adsorption $$\Delta S < 0$$   and for a spontaneous change $$\Delta G = - ve$$
hence $$\Delta H$$  should be highly negative which is clear from the equation
$$\eqalign{ & \Delta G = \Delta H - T\Delta S \cr & = - \Delta H - T\left( { - \Delta S} \right) \cr & = - \Delta H + T\Delta S \cr} $$
So if $$\Delta H$$  is highly negative $$\Delta G$$  will also be $$\left( { - ve} \right)$$

The extent of adsorption increases with decrease in temperature.

Adsorption is a spontaneous process that occurs with release in energy and decrease in the randomness (i.e. entropy) of the adsorbed substance. For a spontaneous process, $$\Delta G$$  must be negative.
$$\Delta G = \Delta H - T\Delta S$$
As the process is exothermic and randomness of molecule (entropy) decreases hence, both $$\Delta H$$  and $$\Delta S$$  will be negative as well.

$$\underset{\begin{array}{l}({\text{More than 10}}^{-6}m\\ \text{or}1000nm)\end{array}}{\text{Suspension}}\text{ > }\underset{\begin{array}{l}(\text{Between}{10}^{-9}\text{to}{10}^{-6}m\\ \text{or}1nm\text{to}1000nm)\end{array}}{\text{colloidal}}>$$           $$\underset{\begin{array}{l}\text{Less than}{10}^{-9}m\\ \text{or}1nm)\end{array}}{\text{true solution}}$$

Molecules of dispersion medium collide with colloidal particles and cause them to move in a zig-zag way.

Graph $$A$$  corresponds to monomolecular adsorption as postulated by Langmuir.
Graph $$C$$  show deviation from Langmuir model. The amount of adsorption keeps on rising with increase in pressure. This is attributed to the formation of additional layers of physically adsorbed gas molecules. Examples - This graphs is furnished by adsorption of nitrogen on an iron or a platinum catalyst at $$ - 195{\,^ \circ }C.$$   Graph $$B$$  and $$D$$  have been observed in those cases in which there is possibility of condensation of gases in the minute capillary pores of the adsorbent at pressure even below the saturation pressure of the gas.

It is zero order reaction
[ NOTE : Adsorption of gas on metal surface is of zero order ]

Zeolites are naturally occurring or synthetic microporous aluminosilicates.

$$\Delta S$$  [change in entropy] and $$\Delta H$$  [ change in enthalpy ] are related by the equation
$$\Delta G = \Delta H - T\Delta S$$
[ Here, $$\Delta G = $$  change in Gibbs free energy ]
For adsorption of a gas, $$\Delta S$$  is negative because randomness decreases. Thus, in order to make $$\Delta G$$  negative [ for spontaneous reaction ], $$\Delta H$$  must be highly negative because reaction is exothermic. Hence, for the adsorption of a gas, if $$\Delta S$$  is negative, therefore, $$\Delta H$$  should be highly negative.

The adsorption of positively charged $$F{e^{3 + }}$$  ions by the sol of hydrated ferric oxide results in positively charged colloid.