Ch 12Surface Chemistry — Class 12 Chemistry, concept-first.

Certain solid surfaces have a natural tendency to grab and hold on to molecules of whatever phase they are exposed to.

It is important not to confuse adsorption with absorption.

Adsorption of gases on solids falls mainly into two types, distinguished by the kind of force holding the gas.

The way the amount of gas adsorbed changes with pressure at a constant temperature is captured by a curve called an adsorption isotherm.

Solids adsorb not only gases but also solutes from solution.

Adsorption underpins a wide range of practical uses:

Some substances can dramatically change the speed of a reaction without being consumed. Heating potassium chlorate decomposes it only slowly, over 653–873 K:

Catalysis splits into two broad classes according to the phases of reactants and catalyst.

1. Diffusion of reactants to the catalyst surface. 2. Adsorption of reactant molecules on the surface. 3. Reaction on the surface via an intermediate. 4.

When a catalyst's action depends on the size of its pores relative to the size of the reactant and product molecules, it is called shape-selective catalysis.

Enzymes are complex nitrogenous organic compounds produced by living plants and animals. They are protein molecules of high molecular mass that form colloidal solutions in water, and they are remarkab…

Catalysts are central to large-scale industrial chemistry. The table below lists some important technical catalytic processes and the catalysts they use:

Solutions are homogeneous, and a suspension (like sand stirred into water) settles out with time. Between these two extremes lies a large family of systems called colloidal dispersions, or simply coll…

Colloids are classified using three criteria:

Since each of the dispersed phase and dispersion medium can be a solid, liquid or gas, eight types of colloidal system are possible.

Depending on how strongly the dispersed phase interacts with the dispersion medium, sols are split into two categories. When water is the medium, the terms become hydrophilic and hydrophobic.

By the nature of the dispersed-phase particles, colloids are of three kinds.

Several important methods produce colloids.

A freshly made colloidal solution usually carries excess electrolyte and other soluble impurities. A trace of electrolyte is needed for stability, but too much coagulates the sol, so the impurities mu…

Colloidal solutions show a distinctive set of properties.

Emulsions are liquid–liquid colloids — fine droplets of one liquid dispersed in another. Shaking two immiscible (or partially miscible) liquids gives a coarse dispersion called an emulsion, and one of…

Colloids are everywhere in daily life — our food, clothes, wooden furniture, houses and newspapers are largely colloidal.