Physical colloid chemistry is a science that studies the chemical and physical properties of surface phenomena and disperse systems.
Definitions
Физколлоидная химия связана с дисперсными systems. They are commonly understood as 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 the dispersed phase is in a fragmented form.
Adsorption and surface phenomena
Physical colloid chemistry examines surface phenomena that occur at the interface of dispersed systems.
Among them we note:
- wetting;
- surface tension;
- adsorption.
Physical colloid chemistry analyzes importanttechnical processes related to wastewater and air purification, mineral processing, metal welding, painting of various surfaces, lubrication, surface cleaning.
Surface tension
Organic and Physical Colloidal Chemistry explainphenomena occurring on the interface. Let us analyze the system, which consists of gas and liquid. The molecule that is inside the system is affected by the forces of attraction from the nearest molecules. The molecule, which is located on the surface, is also affected by forces, but they are not compensated.
The reason is that in the gaseous statethe distances between the molecules are quite large, the forces are almost minimal. The internal pressure is trying to tighten the depth of the fluid molecule, as a result, compression occurs.
To create a new interface, toFor example, stretching into a film, you need to do 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.
Basics of Thermodynamics
The main tasks of physical and colloid chemistry include the calculation by thermodynamic equations. Depending on the reaction, it is possible to determine the possibility of its spontaneous flow.
Due to the instability of thermodynamic systems, processes are taking place that are associated with the enlargement of particles, accompanied by a decrease in the interface.
The reasons for the change in thermodynamic state
What factors affect the amount of surface tension?
First of all, it is important to distinguish the nature of substances.The magnitude of the surface tension is directly related to the peculiarities of the condensed phase. As the polarity of the bond increases in a substance, the tension force increases.
The temperature also affects the state at the interface. In the case of its increase, the forces acting between the individual particles are reduced in the substance.
The concentration of substances dissolved in the analyzed liquid also affects the state of the thermodynamic system.
There are two types of substances.TID (surface inactive substances) increase the magnitude of 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. With the increase of these substances in the solution, their concentration in the surface layer of the solution is observed. Polar organic compounds are acids, alcohols. They incorporate polar groups (amino, carboxyl, hydroxo), as well as a non-polar hydrocarbon chain.
Sorption features
Physical colloid chemistry (STR) includes a section,concerning sorption processes. Adsorption is the process of spontaneous change in the surface layer of the concentration of substances relative to their quantity in the bulk of the phases.
An adsorbent is a substance on the surface.which is carried out deposition. An adsorbing is a substance capable of precipitating. The adsorbate is a precipitated substance. Desorption is the reverse process of adsorption.
Sorption types
Lecturer in Physicolloid Chemistry talks abouttwo types of adsorption. In the case of physical deposition, a small amount of energy is released, which is comparable to the heat of condensation. This process is reversible. In the case of an increase in temperature, adsorption decreases, and the rate of the reverse process (desorption) increases.
Химический вариант адсорбции необратим, с surface does not adsorbtive, and the surface compound. When chemisorption heat is high, it is commensurate with the size of the thermal effect of a chemical reaction. With an increase in temperature, chemisorption increases, the interaction between substances increases.
As an example of chemisorption, we note adsorptionthe surface of the metal is oxygen from the air; it is studied by physical-colloid chemistry. Tasks and solutions are often associated with determining the amount of tension that occurs at the interface between two media.
Чтобы количественно описать ярко выраженную adsorption, use absolute adsorption. It characterizes the amount of adsorbate (in mol) per unit area of the adsorbent taken. Physical and colloid chemistry plans include a quantitative determination of this quantity.
Characteristics of adsorbents
Physical and colloid chemistry special attentiondevotes to the analysis of the types of adsorbents, their practical application. Depending on the size of the surface of the adsorbent, there may be a different amount of adsorbed substance. The most effective adsorbents are considered to be substances having a developed surface: colloids, powders, porous reagents.
As the main quantitative characteristicsadsorbents secrete specific surface area and bulk porosity. The first value shows the ratio of the surface of the adsorbent to the mass. The second characteristic assumes the features of its structure.
In colloid chemistry, there are two varieties.adsorbents. Non-porous substances are created by solid particles forming the porous structure of the “powder diaphragm” with dense packing. The gaps between the grains of the substance act as pores between them. The structure may have a micro or macroporous structure. Porous adsorbents are structures that consist of grains having an internal porosity.
In physical chemistry, special attention is paid tocharacteristic of coarse systems. They are powder formulations, which are formed from powder grains during pressing or packing them tightly into tubes. The resulting systems have certain thermodynamic characteristics, the study of which is the main task of physical colloid chemistry.
There is a process unit (subject tothe nature of the adsorptive) on ionic, molecular, colloidal adsorption. The molecular process is associated with solutions of weak electrolytes or dielectrics. Adsorption of the dissolved substances on the surface of the solid adsorbent occurs.
Part of the active centers on the surface of the adsorbent is occupied by solvent molecules. During the process of deposition, the solvent molecules and the adsorptive compete.
Conclusion
Physical and colloidal chemistry are important.sections of chemistry. They explain the main processes occurring in solutions, allow calculations of the quantities of heat released (absorbed) during the formation of new substances. The basic law used in carrying out quantitative calculations is the Hess law. He connects several thermodynamic characteristics inherent in substances: enthalpy, entropy, energy. The thermodynamic process of formation of complex substances from simple (initial) components can be considered from the point of view of the Hess law. The calculations allow us to determine the effectiveness of the process.
