Diffusion in gases, liquids and solids. Simple diffusion Diffusion in physics: definition

To understand what diffusion depends on, let's consider the factors that influence it.

Diffusion depends on temperature. The rate of diffusion will increase with increasing temperature, because as the temperature increases, the speed of movement of the molecules will increase, that is, the molecules will mix faster. (You all know that sugar takes a very long time to dissolve in cold water)

And when adding external influence(a person stirs sugar in water) diffusion will proceed faster. State of matter will also affect what diffusion depends on, namely the rate of diffusion. Thermal diffusion depends on the type of molecules. For example, if an object is metal, then thermal diffusion occurs faster, unlike if the object were made of a synthetic material. Diffusion between solid materials occurs very slowly.

So the rate of diffusion depends on: temperature, concentration, external influences, state of aggregation of the substance

Diffusion is of great importance in nature and in human life.

Examples of diffusion

To better understand what diffusion is, let's look at it with examples. Let's together give examples of the process of diffusion in gases. Variants of manifestation of this phenomenon may be as follows:

Spreading the scent of flowers;

Spreading the smell of grilled chicken, which puppy Antoshka likes so much;

Tears over chopping onions;

A trail of perfume that can be felt in the air.

The gaps between particles in the air are quite large, the particles move chaotically, so the diffusion of gaseous substances occurs quite quickly.

A simple and accessible example of the diffusion of solids is to take two pieces of multi-colored plasticine and knead them in your hands, observing how the colors mix. And, accordingly, without external influence, if you simply press two pieces against each other, it will take months or even years for the two colors to mix at least a little, so to speak, to penetrate one into the other.

The manifestations of diffusion in liquids can be as follows:

Dissolving a drop of ink in water;

- “The linen has faded” the color of wet fabrics;

Pickling vegetables and making jam

So, diffusion is the mixing of molecules of a substance during their random thermal movement.

Purpose of the work: to prove that diffusion depends on temperature; oo consider examples of diffusion in home experiments; oo make sure that diffusion occurs differently in different substances.

Relevance: Diffusion proves that bodies are composed of molecules that are in random motion; diffusion is of great importance in human life, animals and plants, as well as in technology

What is diffusion?

Diffusion is the spontaneous mixing of contacting substances, occurring as a result of the chaotic (disorderly) movement of molecules.

Another definition: diffusion diffusio - distribution, spreading, dispersion) - the process of transferring matter or energy from an area of ​​high concentration to an area of ​​low concentration.

The most famous example of diffusion is the mixing of gases or liquids (if ink is dropped into water, the liquid will become uniformly colored after some time).

Diffusion occurs in liquids, solids and gases. Diffusion occurs most quickly in gases, slower in liquids, and even slower in solids, which is due to the nature of the thermal movement of particles in these media. The trajectory of each gas particle is a broken line, because during collisions the particles change the direction and speed of their movement. For centuries, workers welded metals and produced steel by heating solid iron in a carbon atmosphere, without having the slightest idea of ​​the diffusion processes occurring during this process. Only in 1896 began studying the problem.

The English metallurgist William Roberts-Austin measured the diffusion of gold in lead in a simple experiment. He fused a thin disk of gold onto the end of a 1 inch (2.45 cm) long cylinder of pure lead, placed the cylinder in a furnace where the temperature was maintained at about 200C, and kept it in the furnace for 10 days. It turned out that a quite measurable amount of gold passed through the entire cylinder. This proves it once again. that the rate of diffusion increases very quickly with increasing temperature. For example, zinc diffuses into copper at 300C almost 100 million times faster than at room temperature.

The diffusion of molecules is very slow. For example, if a piece of sugar is placed at the bottom of a glass of water and the water is not stirred, it will take several weeks before the solution becomes homogeneous.

Does diffusion depend on temperature?

The phenomenon of diffusion can be observed at home when brewing tea. During the experiment, two glasses with cold and hot water were used. When brewing tea, it was found that in a glass of hot water the brewing process was faster.

At home, the phenomenon of diffusion manifests itself everywhere. When mom is in the kitchen chopping onions, cooking chicken, cooking dinner or preparing a marinade for pouring vegetables, the aromas from the kitchen spread throughout the apartment.

I studied the dependence of the speed of spread of the aroma of perfume in a room on temperature: the aroma of perfume spread from one part of the room to another in 20.53 seconds. ; then I sprayed perfume near the table lamp, time - 14.03 seconds.

Conclusion: The rate of diffusion increases with temperature, as the speed of movement of molecules increases.

Diffusion is all around us.

When the rays of the sun enter the room, you can observe a peculiar >.

On this occasion, Lucretius Carus wrote:

Look at this: whenever the sunlight comes through

It cuts through the darkness into our homes with its rays,

Many bodies in the void, you will see, flickering,

They rush back and forth in the radiant glow of light.

As if in an eternal struggle they fight in battles and battles,

They suddenly rush into battles in detachments, without knowing peace.

Thanks to diffusion, indoor dust particles contain mold particles and molecules of heavy metals that are found in furniture, finishing materials and other household items. Indoor flowers can easily cope with toxic substances dissolved in the air of rooms: nephrolepis, dieffenbachia, spurge, ivy, pelargonium, sansevieria, etc. And all this happens thanks to diffusion

The well-known agave (aloe) can reduce the number of harmful microbes by 4 times, and the prickly pear cactus reduces the number of molds in the air by 6-7 times. Tobacco smoke and linoleum coatings are harmful to our health. Indoor plants (ficus benjamina, tradescantia, chlorophytum) can absorb and decompose toxic substances.

Diffusion studies in vegetables.

Apple experiment

Different varieties of apples were used: >, >, >.

In apples of the > variety, the penetration of manganese was slower. This variety of apples is winter, perhaps it is less juicy, and their structure is more dense.

Experience with vegetables

The following vegetables were used for the experiment: turnips, carrots, zucchini, potatoes

After three hours, it was found that the penetration of manganese in squash and potatoes was greater than in turnips and carrots. Turnips and carrots have a denser structure, and the penetration depth of manganese particles was less.

Diffusion and safety

The flammable propane gas we use at home for cooking has no color. Therefore, it would be difficult to immediately notice a gas leak. And when there is a leak, the gas spreads throughout the room due to diffusion. and we smell this leak. Meanwhile, at a certain ratio of gas to air in a closed room, a mixture is formed that can explode. For example, from a lit match. The gas can also cause poisoning to people.

Conclusions: oo During diffusion, particles of one substance penetrate into the spaces between particles of another substance, and the substances mix.

oo The rate of diffusion increases with increasing temperature.

oo Diffusion is of great importance in the life processes of humans, animals and plants.

Osmosis is the diffusion of water through a semi-permeable membrane separating two solutions, from a lower concentration to a higher one.[...]

At the beginning of the third period, the diffusion of water usually occurs without much difficulty. However, as the wood dries, the rate of diffusion decreases so much that a dry layer forms on the surface of the wood. Thus, the main condition on which the drying rate in the third period depends is the diffusion of water inside the dried wood. Compared to the value of diffusion, the delaying role of the gas film now becomes insignificant. In the same way, the coolant velocity and the partial pressure of water vapor have only a minor influence on the process.[...]

Nature of the disease. The disease involves the diffusion of water from the body into the intestinal tract. The amount of this diffusing water is colossal (about 30 l/day), and therefore it is continuously excreted in the form of vomiting and loose stools. As a result, dehydration of the body occurs, the intensity of oxidative processes rapidly decreases, and tissues are saturated with products of incomplete combustion and carbon dioxide. The incubation period is about three days.[...]

Osmotic pressure is the pressure that results from the diffusion of water through a membrane (from a lower concentration of a solution to a higher one). [...]

An increase in the relative number of mobile monomeric water molecules and the activity of hydroxyl ions in relation to hydrogen ions apparently causes the acceleration of water diffusion, which affects the processes of osmosis, which are of great importance for the life of plant and animal organisms. [...]

In other papers, researchers concluded that the sulfo group anion in the cation exchanger binds three water molecules. Apparently, the difference in results largely depends on the difference in methods for assessing the amount of hydration of ionized groups in the ion-exchange resin. In any case, it has been established quite precisely that sulfonic cation exchangers in the H+ form swell more strongly than in salt forms, while weakly acidic cation exchangers, which are practically not ionized in the H form, swell predominantly in salt forms. For the same reason, weakly basic anion exchangers swell in salt forms also much more strongly than in the OH form. Non-ion exchange transfer of electrolytes towards water diffusion when establishing osmotic equilibrium of ion exchanger grains with an external solution in dilute solutions does not have any significant effect on the behavior of ion exchange resins during water desalting or regeneration of ion exchange filters. With an increase in the concentration of acids and alkalis in regeneration solutions, this non-ion exchange transfer of electrolytes turns out to be so significant that it cannot be neglected. [...]

It is well known that in some hydrates there is only a ring or only a vacancy diffusion mechanism that is not associated with disorder. In these cases, diffusion is observed, as a rule, only at high temperatures. In this crystal, water molecules are arranged in six zigzag rings, as if carved from the structure of ice. The axes of all rings are parallel to each other, and the H-II directions form an angle of 47° with the axes of the rings. From here, according to the rules for averaging dipole interaction, one can find the averaged constant of this interaction - 9 kHz. Measurements have shown that in dNoptase, diffusion is observed only at temperatures above +120°C, and the characteristic frequency is exactly 9 kHz. For apophyllite, another hydrated silicate, diffusion begins at 170°C; calculation and experiment give almost identical values ​​with a frequency characteristic of -6.5 kHz. In patrolite, water diffusion at +150°C averages the dipole-dipole interaction to zero in complete agreement with the expected value due to the fact that in this crystal the angle between the H-H vectors and the symmetry axis is almost equal to the magic one. [...]

Champetier and Bonnet argued that there was selective absorption of acid by cotton. Kazbekar and Nil discovered the selective absorption of water by cellophane when swelling in acid solutions due to the faster diffusion of water compared to the acid into the film. A detailed study of the selective absorption of water and acid has not been carried out.[...]

Membrane (from Latin membrana - membrane) - a thin film or plate, usually fixed along the contour; osmosis (from the Greek osmos - push, pressure) - one-way diffusion of water through a semi-permeable partition (membrane) separating the solution from pure water or a solution of lower concentration; ultrafiltration (from Latin ultra - above, beyond) - separation of solutions and colloidal systems using semi-permeable membranes in special devices under a pressure of 0.1 - 0.8 MPa. [...]

At temperatures above 200-250 K, the NMR spectra of wide-pore zeolites narrow sharply (hundreds of times) and acquire a structure characteristic of water diffusing in crystals. In this case, two facts are significant. Firstly, the width of the narrowed spectrum remains constant up to the dehydration temperature (200-300°C or more). This means that at all temperatures the molecule moves along the same diffusion path strictly specified by the crystal structure, exactly the same as in crystalline hydrates. Secondly, despite the low-temperature mobility, very high dehydration temperatures remain. This feature sharply distinguishes zeolites from crystalline hydrates, in which dehydration or melting rarely occurs at temperatures significantly above 100°C. The nature of the high-temperature hydrated state of zeolites became clear only after the discovery of the “two-phase” structure of zeolite water. It turned out that the diffusion of water molecules in zeolite channels does not prevent some of these molecules from being rigidly bound in zeolite channels. For example, in mordenite, despite the onset of diffusion narrowing of the NMR spectrum at -100°C, even at +100°C about 10% of rigidly bound water remains (while complete dehydration occurs only at 450°C). It was assumed that these tightly bound molecules, like plugs, block the zeolite channel, blocking the path of diffusing molecules. From here it is natural to put forward an isochoric model of zeolite water in a closed space of channels. Heating increases the pressure inside the channel, and along with the pressure, the “melting” temperature of zeolite water also increases. In accordance with the above, the diffusion of water in hydrated zeolites can be considered as isochoric (in a closed volume) melting. It is also obvious that the effectiveness of “plugs” in blocking the channel volume is associated with their collective properties resulting from the presence of stronger water-water bonds in certain areas of the zeolite channels.[...]

Comparison with experience both confirms and does not confirm these expectations. But for some reason, hydrates of chlorides and bromides of calcium, strontium and barium fall out of the pattern, in which, despite everything, the diffusion of water is not detected until melting.[...]

The possibility of using calcium and zinc ferrites in primers along with anti-corrosion pigments to replace toxic and expensive lead and chromium based pigments has been studied. Primers containing calcium and zinc ferrites present a greater barrier to water and oxygen diffusion than coatings pigmented with iron oxide. In alkyd paints, calcium ferrite is more effective. The ratio between inert pigment and calcium ferrite in primers is 60:40. In chlorinated rubber paints, zinc ferrite is more effective, and the ratio between inert pigment and zinc ferrite is 80:20-70:30. It is noted that the protective effect of calcium and zinc ferrites is weaker than that of classical anti-corrosion pigments.[...]

Another theory better explains the mechanism of poisoning of living organisms, according to which poisoning occurs as a result of mercury and copper ions entering the respiratory or digestive organs, as a result of which the protein of these organs coagulates and the organism dies. According to this theory, the protective effect of mercuric oxide and cuprous oxide is explained as follows. Due to the diffusion of seawater into the paint film, mercury oxide and cuprous oxide are exposed to NaCl contained in seawater. As a result of this influence, as indicated above, a salt of complex composition 6MaCl13HCHCuCl2 is formed. A solution of this salt containing mercury and copper ions, slowly diffusing in the direction opposite to the diffusion of water, creates a zone in the immediate vicinity of the ship that is toxic for representatives of marine fauna. This zone becomes toxic, as mentioned above, even with a small content of mercury ions in the water and copper. With this mechanism of action of mercury oxide and cuprous oxide, all the simplest animal organisms that enter the zone poisoned by mercury and copper ions die and only individual specimens can accidentally approach the ship. Continuous fouling can begin only after a significant depletion of the outer layer of paint in mercury and copper. In practice, such a course of the process of fouling of a vessel is observed - fouling begins with the settlement of individual specimens of mollusks, and continuous fouling, much less intense than when using conventional paint, begins much later than in the case of painting a vessel with ordinary oil paint.