Organic and physicolloid chemistry: description, tasks and features

Fizkolloidnaya chemistry is a science that studies the chemical and physical properties of surface phenomena and disperse systems.

Definitions

Physicocidal chemistry is associated with dispersive systems. They are understood to mean such states in which one or more substances are in a dispersed (fragmented) state by the mass of the second substance. The fragmented phase is called the dispersed phase. A dispersion medium is a medium in which a dispersed phase is present in a fragmented form.

Adsorption and surface phenomena

Physicoidal chemistry considers surface phenomena that occur at the interface of disperse systems.

Among them we note:

• Wetting;
• surface tension;
• Adsorption.

Fizkolloidnaya chemistry analyzes important technical processes related to wastewater and air purification, mineral processing, welding of metals, dyeing of different surfaces, lubrication, cleaning surfaces.

Surface tension

Organic and fizkolloidnaya chemistry explains the phenomena occurring at the interface of phases. Let us analyze the system, which consists of gas and liquid. The molecule, which is located inside the system, is acted upon by attractive forces from the nearest molecules. The molecule that is located on the surface also has the effect of force, but they are not compensated.

The reason is that in the gaseous state the distances between the molecules are sufficiently large, the forces are practically minimal. Internal pressure tries to tighten deep into the molecule of the liquid, as a result, compression occurs.

To create a new phase interface, for example, stretching into a film, it is necessary to work against internal pressure. There is a direct relationship between the energy expended and the internal pressure. Energy, concentrated in molecules located on the surface, is considered free surface energy.

Fundamentals of thermodynamics

The main tasks of fizkolloidnoy chemistry include the calculation of thermodynamic equations. Depending on the considered reaction, it is possible to determine the possibility of its spontaneous flow.

Because of the instability of thermodynamic systems, processes occur that are associated with the coarsening of particles, accompanied by a decrease in the phase interface.

The causes of the change in the thermodynamic state

What factors affect the amount of surface tension?

First of all, it is important to distinguish the nature of the substances. The magnitude of the surface tension is directly related to the features of the condensed phase. With an increase in the polarity of the bond, an increase in the tension force occurs in the substance.

The temperature also affects the state at the interface. In the case of its increase, the forces acting between the individual particles decrease in the substance.

The concentration of substances dissolved in the liquid being analyzed also affects the state of the thermodynamic system.

There are two kinds of substances. PIV (surface-inactive substances) increase the tension of the solution in comparison with the ideal solvent. Such substances are strong electrolytes. Surfactants (surfactants) reduce the amount of tension at the interface in the resulting solution. When these substances increase in solution, their concentration in the surface layer of the solution is observed. Polar organic compounds are acids, alcohols. They have in their composition polar groups (amino, carboxyl, hydroxo), and also a nonpolar hydrocarbon chain.

Features of sorption

Fizkolloidnaya chemistry (STR) includes a section on sorption processes. Adsorption is a process of spontaneous change in the surface layer of the concentration of substances relative to their quantity in the volume of phases.

Adsorbent is a substance on the surface of which precipitation is carried out. Adsorptive is a substance capable of precipitation. Adsorbate is a precipitated substance. Desorption is the reverse of adsorption.

Types of sorption

Teacher fizkolloidnoy chemistry talks about two types of adsorption. In the case of physical deposition, a small amount of energy is released, which is comparable with the heat of condensation. This process is reversible. In the case of temperature increase, adsorption decreases, the rate of the reverse process (desorption) increases.

The chemical variant of adsorption is irreversible, surface adsorption does not leave the surface, but a surface compound. During chemisorption, the heat is high, it is commensurable with the size of the thermal effect of the chemical reaction. With an increase in the temperature, chemisorption increases, and the interaction between substances increases.

As an example of chemisorption, we note the adsorption of oxygen from the air by the metal surface, it is studied by physicoid chemistry. Problems and solutions are often associated with the determination of the value of the tension arising at the interface between two media.

To quantify the pronounced adsorption, absolute adsorption is used. It characterizes the amount of adsorbate (in moles) per unit area of the adsorbent taken. The plans for physical chemistry include the quantitative determination of this quantity.

Characteristics of adsorbents

Physical and colloid chemistry pays special attention to the analysis of types of adsorbents, their practical application. Depending on the size of the surface of the adsorbent, a different amount of adsorbed material is possible. The most effective adsorbents are substances having a developed surface: colloids, powders, porous reagents.

As the main quantitative characteristics of adsorbents, the specific surface and volumetric porosity are isolated. The first value shows the ratio of the surface of the adsorbent to the mass. The second characteristic assumes the features of its structure.

Two types of adsorbents are distinguished in colloid chemistry. Nonporous substances are created by solid particles, forming a porous structure of a "powder diaphragm" with close packing. As the pores between them protrude the gaps between the grains of matter. The structure may have a micro- or macroporous structure. Porous adsorbents are structures that consist of grains having internal porosity.

In physical chemistry, special attention is paid to the characterization of coarsely dispersed systems. They are powder formulations that are formed from powder grains when pressed or densely packed into tubes. The obtained systems have definite thermodynamic characteristics, the study of which is the main task of physicoid chemistry.

There is a process subdivision (taking into account the nature of the adsorbent) for ionic, molecular, colloidal adsorption. Molecular process is associated with solutions of weak electrolytes or dielectrics. There is adsorption of dissolved substances on the surface of solid adsorbent.

Part of the active sites on the adsorbent surface are occupied by solvent molecules. During the passage of the precipitation process, the molecules of the solvent and adsorptive act as competitors.

Conclusion

Physical and colloid chemistry are important sections of chemistry. They explain the main processes occurring in solutions, allow calculations of the amounts of heat released (absorbed) during the formation of new substances. The main law used in making quantitative calculations is the law of Hess. It relates several thermodynamic characteristics inherent in substances: enthalpy, entropy, energy. The thermodynamic process of the formation of complex substances from simple (initial) components can be considered from the standpoint of Hess's law. The calculations carried out make it possible to determine the efficiency of the process.