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 this object were made of synthetic material. Diffusion between solid materials occurs very slowly.

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

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.

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Geller and Tak-Go Sun explain the dependence of the diffusion rate on the composition of steel by the fact that the presence in the metal of additives that have a greater or lesser affinity for hydrogen than iron leads to a corresponding change in the diffusion coefficient, and therefore to a change in the activation energy of the diffusion process.  

The dependence of the rate of diffusion of low molecular weight substances in crystallizing copolymers on the chain composition is shown in Fig. 5.14, 5.15. It can be seen that as the matrix amorphizes, the differences between DKP and Al decrease, and in the middle range of copolymer compositions (/cr 0) they coincide with each other.  

The dependence of the rate of diffusion of impurity elements in a solid solvent on the grain size is well known.  

Due to the dependence of the diffusion rate on temperature, the ability of OM to penetrate into varnish and other coatings is winter conditions very low. For example, at - 10 C, practically OM does not penetrate into paint and varnish coatings.  

Since the dependence of the rates of diffusion and relaxation on temperature and concentration is not the same, under the same temperature and concentration conditions C. Therefore, with a change in temperature and concentration, a transition from C is possible.  

Since the dependence of the rates of diffusion and relaxation on temperature and concentration is not the same, under the same temperature and concentration conditions C. Therefore, with a change in temperature and concentration, a transition from C is possible.  

Present a graph of diffusion rate versus velocity chemical reaction on temperature for a heterogeneous reaction and indicate in which temperature range the reaction occurs in the diffusion region, and in which in the kinetic region.  

It is very important to know the dependence of the diffusion rate on the arc diameter.  

It is also easy to explain the dependence of the diffusion rate on temperature. Higher temperature means higher molecular speeds and faster diffusion. The presence of temperature gradients leads to thermal diffusion. The phenomenon of thermal diffusion is that the presence of a temperature gradient in a mixture of two gases leads to the emergence of a gradient in the relative concentrations of these components. If the mixture as a whole is at rest, the concentration gradient at equilibrium will be such that the action of thermal diffusion is balanced by the action of ordinary diffusion.  

It is also easy to understand the dependence of the diffusion rate on temperature and pressure. Higher temperature means higher molecular speeds and faster diffusion. More high blood pressure means shorter free path length and slower diffusion.  

It is also easy to understand the dependence of the diffusion rate on temperature. Higher temperature means higher molecular speeds and faster diffusion. The presence of temperature gradients leads to thermal diffusion. The phenomenon of thermal diffusion is that the presence of a temperature gradient in a mixture of two gases leads to the emergence of a gradient in the relative concentrations of these components.  

IN this work The dependence of the rate of diffusion of copper ions into glass on the nature and amount of alkali oxides in the glass, as well as on the nature of the oxides of alkaline earth elements, was determined.  

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Diffusion plays huge role in nature, in human life and in technology. Diffusion processes can have both positive and negative influence on the life activity of humans and animals. An example of a positive impact is maintaining a uniform composition atmospheric air near the Earth's surface. Diffusion plays an important role in various fields of science and technology, in processes occurring in living and inanimate nature. It influences the course of chemical reactions.

With the participation of diffusion or when this process is disrupted and changed, negative phenomena in nature and human life can occur, such as extensive pollution of the environment with the products of human technical progress.

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

Target:

prove that diffusion depends on temperature;

consider examples of diffusion in home experiments;

make sure that diffusion in different substances happens in different ways.

Consider the thermal diffusion of substances.

Research objectives:

Study scientific literature on the topic “Diffusion”.

Prove the dependence of the diffusion rate on the type of substance and temperature.

Study the influence of the diffusion phenomenon on the environment and humans.

Describe and design the most interesting experiments by diffusion.

Research methods:

Analysis of literature and Internet materials.

Conducting experiments to study the dependence of diffusion on the type of substance and temperature.

Analysis of results.

Subject of research: the phenomenon of diffusion, the dependence of the course of diffusion on various factors, the manifestation of diffusion in nature, technology, and everyday life.

Hypothesis: Diffusion is of great importance for humans and nature.

1.Theoretical part

1.1.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 ( lat. diffusio- spreading, spreading, dissipation) - 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, 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 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.

1.2. The role of diffusion in nature

With the help of diffusion, various gaseous substances spread in the air: for example, the smoke of a fire spreads over long distances. If you look at the chimneys of businesses and the exhaust pipes of cars, in many cases you can see smoke near the pipes. And then he disappears somewhere. Smoke dissolves in the air due to diffusion. If the smoke is dense, then its plume stretches quite far.

The result of diffusion can be equalization of the temperature in the room during ventilation. This is how air pollution occurs harmful products industrial production and vehicle exhaust gases. The natural flammable gas we use at home is colorless and odorless. If there is a leak, it is impossible to notice it, so at distribution stations the gas is mixed with a special substance that has a sharp, unpleasant smell, which is easily felt by a person even at a very low concentration. This precaution allows you to quickly notice the accumulation of gas in the room if a leak occurs (Figure 1).

Thanks to the phenomenon of diffusion, the lower layer of the atmosphere - the troposphere - consists of a mixture of gases: nitrogen, oxygen, carbon dioxide and water vapor. In the absence of diffusion, stratification would occur under the influence of gravity: below there would be a layer of heavy carbon dioxide, above it - oxygen, above - nitrogen, inert gases (Fig. 2).

We also observe this phenomenon in the sky. Dispersing clouds are also an example of diffusion, and as F. Tyutchev accurately said about this: “Clouds are melting in the sky...” (Fig. 3)

The principle of diffusion is based on the mixing of fresh water with salt water when rivers flow into the seas. Diffusion of solutions various salts in the soil contributes to normal plant nutrition.

Diffusion plays an important role in the life of plants and animals. Ants mark their path with droplets of odorous liquid and find out the way home (Figure 4)

Thanks to diffusion, insects find their food. Butterflies, fluttering between plants, always find their way to beautiful flower. Bees, having discovered a sweet object, storm it with their swarm. And the plant grows and blooms for them, too, thanks to diffusion. After all, we say that the plant breathes and exhales air, drinks water, and receives various microadditives from the soil.

Carnivores also find their victims through diffusion. Sharks can smell blood from several kilometers away, just like piranha fish (Figure 5).

Diffusion processes play a major role in the supply of oxygen to natural reservoirs and aquariums. Oxygen reaches deeper layers of water in stagnant waters due to diffusion through their free surface. For example, leaves or duckweed covering the surface of the water can completely stop the access of oxygen to the water and lead to the death of its inhabitants. For the same reason, vessels with a narrow neck are unsuitable for use as an aquarium (Fig. 6).

It has already been noted that there is much in common in the meaning of the phenomenon of diffusion for the life of plants and animals. First of all, it should be noted the role of diffusion exchange through the surface of plants in the performance of the respiratory function. For trees, for example, it is especially observed great development surface (leaf crown), since diffusion exchange through the surface of the leaves performs the function of respiration. K.A. Timiryazev said: “Whether we talk about the nutrition of the root due to the substances found in the soil, whether we talk about the aerial nutrition of the leaves due to the atmosphere or the nutrition of one organ at the expense of another, neighboring one - everywhere we will resort to the same reasons for explanation : diffusion" (Figure 7).

Thanks to diffusion, oxygen from the lungs penetrates into the human blood, and from the blood into the tissues.

In the scientific literature, I studied the process of one-way diffusion - osmosis, i.e. diffusion of substances through semipermeable membranes. The process of osmosis differs from free diffusion in that at the border of two contacting liquids there is an obstacle in the form of a partition (membrane), which is permeable only to the solvent and not at all permeable to molecules of the dissolved substance (Fig. 8).

Soil solutions contain mineral salts and organic compounds. Water from the soil enters the plant by osmosis through the semi-permeable membranes of the root hairs. The concentration of water in the soil is higher than inside the root hairs, so water penetrates into the grain and gives life to the plant.

1.3. The role of diffusion in everyday life and technology

Diffusion is used in many technological processes: salting, obtaining sugar (sugar beet shavings are washed with water, sugar molecules diffuse from the shavings into the solution), making jam, dyeing fabrics, washing things, cementation, welding and soldering of metals, including diffusion welding in a vacuum (metals that are otherwise methods cannot be combined - steel with cast iron, silver with stainless steel, etc.) and diffusion metallization of products (surface saturation of steel products with aluminum, chromium, silicon), nitriding - saturation of the steel surface with nitrogen (steel becomes hard, wear-resistant), carburization - saturation of steel products with carbon, cyanidation - saturation of the steel surface with carbon and nitrogen.

The spread of odors in the air is the most common example of diffusion in gases. Why does the smell spread not instantly, but after some time? The fact is that while moving in a certain direction, molecules of an odorous substance collide with air molecules. The trajectory of each gas particle is a broken line, because During collisions, particles change the direction and speed of their movement.

2. Practical part

How many amazing and interesting things are happening around us! I want to know a lot, try to explain it myself. It was for this reason that I decided to conduct a series of experiments, during which I tried to find out whether the diffusion theory is really valid and whether it is confirmed in practice. Any theory can be considered reliable only if it is repeatedly confirmed experimentally.

Experiment No. 1 Observation of the phenomenon of diffusion in liquids

Target: study diffusion in liquid. Observe the dissolution of pieces of potassium permanganate in water at a constant temperature (at t = 20°C)

Devices and materials: glass of water, thermometer, potassium permanganate.

I took a piece of potassium permanganate and two glasses of clean water at a temperature of 20 °C. She put pieces of potassium permanganate into glasses and began to observe what was happening. After 1 minute, the water in the glasses begins to color.

Water is good solvent. Under the influence of water molecules, the bonds between the molecules of the solid substances of potassium permanganate are destroyed.

In the first glass I did not stir the solution, but in the second I did. By stirring the water (shaking), I made sure that the diffusion process occurs much faster (2 minutes)

The color of the water in the first glass becomes more intense as time passes. Water molecules penetrate between the potassium permanganate molecules, breaking the attractive forces. Simultaneously with the attractive forces between the molecules, repulsive forces begin to act and, as a result, destruction occurs crystal lattice solid matter. The process of dissolving potassium permanganate is over. The experiment took 3 hours and 15 minutes. The water turned completely crimson (Figure 9-12).

It can be concluded that the phenomenon of diffusion in a liquid is a long-term process, as a result of which solids dissolve.

I wanted to find out what else the speed of diffusion depends on.

Experiment No. 2 Study of the dependence of the diffusion rate on temperature

Target: study how water temperature affects the rate of diffusion.

Devices and materials: thermometers - 1 piece, stopwatch - 1 piece, glasses - 4 pieces, tea, potassium permanganate.

(experience of preparing tea at an initial temperature of 20°C and at a temperature of 100°C in two glasses).

We took two glasses of water at t=20 °C and t=100 °C. The figures show the progress of the experiment after a certain time from the beginning: at the beginning of the experiment - Fig. 1, after 30 s. - Fig. 2, after 1 minute. - Fig. 3, after 2 minutes. - Fig.4, after 5 minutes. - rice 5, after 15 minutes. - Fig. 6. From this experience we can conclude that the rate of diffusion is affected by temperature: the higher the temperature, the higher the rate of diffusion (Figure 13-17).

I got the same results when I took 2 glasses of water instead of tea. One of them contained water at room temperature, the second had boiling water.

I put the same amount of potassium permanganate into each glass. In the glass where the water temperature was higher, the diffusion process proceeded much faster (Fig. 18-23.)

Therefore, the rate of diffusion depends on temperature - the higher the temperature, the more intense the diffusion occurs.

Experiment No. 3 Observation of diffusion using chemical reagents

Target: Observing the phenomenon of diffusion at a distance.

Equipment: cotton wool, ammonia, phenolphthalein, test tube.

Description of the experience: Pour ammonia into the test tube. Moisten a piece of cotton wool with phenolphthalein and place it on top of the test tube. After some time, we observe the coloring of the fleece (Fig. 24-26).

The ammonia evaporates; molecules ammonia penetrated the cotton wool soaked in phenolphthalein, and it became colored, although the cotton wool was not brought into contact with alcohol. The alcohol molecules mixed with air molecules and reached the cotton wool. This experiment demonstrates the phenomenon of diffusion at a distance.

Experience No. 4. Observation of the phenomenon of diffusion in gases

Target: study of changes in gas diffusion in the air depending on changes in room temperature.

Devices and materials: stopwatch, perfume, thermometer

Description of the experience and results obtained: I studied the time of propagation of the smell of perfume in the office V = 120 m 3 at a temperature t = +20 0. The time was recorded from the beginning of the spread of the smell in the room until obvious sensitivity was obtained in people standing at a distance of 10 m from the object under study (perfume). (Figure 27-29)

Experiment No. 5 Dissolving pieces of gouache in water at a constant temperature

Target:

Devices and materials: three glasses, water, gouache of three colors.

Description of the experience and results obtained:

They took three glasses, filled with water t = 25 0 C, and threw identical pieces of gouache into the glasses.

We began to observe the dissolution of the gouache.

Photos were taken after 1 minute, 5 minutes, 10 minutes, 20 minutes, dissolution ended after 4 hours 19 minutes (Figure 30-34)

Experiment No. 6 Observation of the phenomenon of diffusion in solids

Target: observation of diffusion in solids.

Devices and materials: apple, potato, carrot, green solution, pipette.

Description of the experience and results obtained:

Cut the apple, carrots, and potatoes into one of the halves.

We observe how the stain spreads across the surface

We cut at the point of contact with the brilliant green to see how deeply it has penetrated inside (Fig. 35-37)

How to conduct an experiment to confirm the hypothesis about the possibility of diffusion in solids? Is it possible to mix substances in such a state of aggregation? Most likely the answer is “Yes”. But it is convenient to observe diffusion in solids (very viscous) using thick gels. This is a dense solution of gelatin. It can be prepared as follows: dissolve 4-5 g of dry edible gelatin in cold water. Gelatin must first swell for several hours, and then it is completely dissolved by stirring in 100 ml of water, lowered into a vessel with hot water. After cooling, a 4-5% gelatin solution is obtained.

Experiment No. 7 Observation of diffusion using thick gels

Target: Observation of the phenomenon of diffusion in solids (using a thick solution of gelatin).

Equipment: 4% gelatin solution, test tube, small crystal of potassium permanganate, tweezers.

Description and result of the experiment: Place the gelatin solution in a test tube; quickly insert a crystal of potassium permanganate into the center of the test tube with tweezers in one motion.

Potassium permanganate crystal at the beginning of the experiment

Location of the crystal in a vial of gelatin solution after 1.5 hours

Within a few minutes, a violet-colored ball will begin to grow around the crystal, and over time it becomes larger and larger. This means that the crystalline substance spreads in all directions at the same speed (Figure 38-39)

In solids, diffusion occurs, but much slower than in liquids and gases.

Experiment No. 8 Temperature difference in liquid - thermal diffusion

Target: Observation of the phenomenon of thermal diffusion.

Equipment: 4 identical glass vessels, 2 paint colors, hot and cold water, 2 plastic cards.

Description and result of the experiment:

1. Add a little red paint to containers 1 and 2, blue paint to containers 3 and 4.

2. Pour hot water into vessels 1 and 2.

3. Pour cold water into vessels 3 and 4.

4. Cover vessel 1 plastic card, turn it upside down and place it on vessel 4.

5. Cover vessel 3 with a plastic card, turn it upside down and place it on vessel 2.

6. Remove both cards.

This experiment demonstrates the effect of thermal diffusion. In the first case, hot water appears on top of cold water and diffusion does not occur until the temperatures are equal. And in the second case, on the contrary, the bottom is hot and the top is cold. And in the second case, the molecules hot water begin to strive upward, and the cold molecules begin to strive downward (Figure 41-44).

Conclusion

During this research work we can conclude that diffusion plays a huge role in the life of humans and animals.

From this research work, it can be concluded that the duration of diffusion depends on temperature: the higher the temperature, the faster the diffusion occurs.

I studied the phenomenon of diffusion using various substances as an example.

The rate of flow depends on the type of substance: it flows faster in gases than in liquids; in solids, diffusion proceeds much more slowly. This statement can be explained as follows: gas molecules are free, located at distances of many more sizes molecules move at high speeds. The molecules of liquids are arranged as randomly as in gases, but much denser. Each molecule, surrounded by neighboring molecules, moves slowly inside the liquid. Molecules of solids vibrate around an equilibrium position.

There is thermal diffusion.

List of used literature

Gendenstein, L.E. Physics. 7th grade. Part 1 / L.E. Gendenshtein, A.B., Kaidalov. - M: Mnemosyne, 2009.-255 p.;

Kirillova, I.G. Physics reading book for 7th grade students high school/ I.G. Kirillova.- M., 1986.-207 p.;

Olgin, O. Experiments without explosions / O. Olgin. - M.: Khimik, 1986.-192 pp.;

Peryshkin, A.V. Physics textbook, grade 7 / A.V. Peryshkin.- M., 2010.-189 p.;

Razumovsky, V.G. Creative problems in physics / V.G. Razumovsky.- M., 1966.-159 p.;

Ryzhenkov, A.P. Physics. Human. Environment: Supplement to the physics textbook for the 7th grade of educational institutions / A.P. Ryzhenkov.- M., 1996.- 120 p.;

Chuyanov, V.A. Encyclopedic Dictionary young physicist / V.A. Chuyanov.- M., 1984.- 352 p.;

Shablovsky, V. Entertaining physics/ V. Shablovsky. S.-P., Trigon, 1997.-416 p.

Application

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Solvent particles (blue) are able to cross the membrane,

solute particles (red) are not.

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Dependence of the rate of diffusion of molecules on the temperature of a substance Dependence of the rate of diffusion of molecules on the temperature of a substance Project author: Maxim Karapuzov, 7th grade student Project author: Maxim Karapuzov, 7th grade student MBOU "SECONDARY EDUCATIONAL SCHOOL 40" BELGORODSKY DISTRICT, STARY OSCOL Supervisor: Gavryushina Lyudmila Konstantinovna , physics teacher, physics teacher, MBOU "SECONDARY SCHOOL 40" BELGORODSKY DISTRICT, STARY Oskol

Problem Statement Why do substances mix? Why do substances mix? What is the role of diffusion in the world around us? What is the role of diffusion in the world around us? What does the process of diffusion depend on? What does the process of diffusion depend on?

Interpretation of results Diffusion is a time process. The duration of diffusion depends on the temperature and type of substance: the higher the temperature, the faster the diffusion process. As a result of the experiments, I was convinced that the hypothesis I put forward was fully confirmed. Indeed, with increasing temperature, the diffusion of molecules in a liquid will occur faster. The more average speed movement of body molecules, the higher its temperature

Among the numerous phenomena in physics, the process of diffusion is one of the simplest and most understandable. After all, every morning, when preparing aromatic tea or coffee, a person has the opportunity to observe this reaction in practice. Let's learn more about this process and the conditions for its occurrence in different states of aggregation.

What is diffusion

This word refers to the penetration of molecules or atoms of one substance between similar structural units of another. In this case, the concentration of penetrating compounds is equalized.

This process was first described in detail by the German scientist Adolf Fick in 1855.

The name of this term was derived from the Latin diffusio (interaction, dispersion, distribution).

Diffusion in liquid

The process under consideration can occur with substances in all three states of aggregation: gaseous, liquid and solid. To find practical examples this, you just need to look into the kitchen.

Borscht simmering on the stove is one of them. Under the influence of temperature, glucosin betanin molecules (the substance that gives beets such a rich scarlet color) evenly react with water molecules, giving it a unique burgundy hue. This case- this is in liquids.

In addition to borscht, this process can also be seen in a glass of tea or coffee. Both of these drinks have such a uniform, rich shade due to the fact that the brew or particles of coffee, dissolving in water, spread evenly between its molecules, coloring it. The action of all popular instant drinks of the nineties is based on the same principle: Yupi, Invite, Zuko.

Interpenetration of gases

Atoms and molecules that carry odor are in active motion and, as a result, mix with particles already contained in the air and are fairly evenly dispersed throughout the room.

This is a manifestation of diffusion in gases. It is worth noting that the inhalation of air itself also relates to the process under consideration, as does the appetizing smell of freshly prepared borscht in the kitchen.

Diffusion in solids

The kitchen table, on which there are flowers, is covered with a bright tablecloth. yellow. It received a similar shade due to the ability of diffusion to occur in solids.

The process of giving the canvas some uniform shade takes place in several stages as follows.

1. Particles of yellow pigment diffused in the dye tank towards the fibrous material.
2. They were then absorbed by the outer surface of the fabric being dyed.
3. The next step was to diffuse the dye again, but this time into the fibers of the fabric.
4. Finally, the fabric fixed particles of pigment, thus becoming colored.

Diffusion of gases in metals

Usually, when talking about this process, we consider the interactions of substances in identical states of aggregation. For example, diffusion in solids, solids. To prove this phenomenon, an experiment is carried out with two metal plates(gold and lead). The interpenetration of their molecules occurs for quite a long time (one millimeter in five years). This process is used to make unusual jewelry.

However, compounds in different states of aggregation are also capable of diffusing. For example, there is diffusion of gases in solids.

During experiments it was proven that a similar process occurs in the atomic state. To activate it, as a rule, a significant increase in temperature and pressure is required.

An example of such gaseous diffusion in solids is hydrogen corrosion. It manifests itself in situations when hydrogen atoms (H 2) arising in the process of some chemical reaction under the influence of high temperatures(from 200 to 650 degrees Celsius) penetrate between the structural particles of the metal.

In addition to hydrogen, diffusion of oxygen and other gases can also occur in solids. This process, invisible to the eye, brings a lot of harm, because metal structures can collapse because of it.

Diffusion of liquids in metals

However, not only gas molecules can penetrate solids, but also liquids. As in the case of hydrogen, most often this process leads to corrosion (if we are talking about metals).

A classic example of liquid diffusion in solids is the corrosion of metals under the influence of water (H 2 O) or electrolyte solutions. For most, this process is more familiar under the name rusting. Unlike hydrogen corrosion, in practice it is encountered much more often.

Conditions for accelerating diffusion. Diffusion coefficient

Having figured out in what substances the process in question can occur, it is worth finding out about the conditions for its occurrence.

First of all, the speed of diffusion depends on the state of aggregation in which the interacting substances are. The larger in which the reaction occurs, the slower its speed.

In this regard, diffusion in liquids and gases will always be more active than in solids.

For example, if crystals of potassium permanganate KMnO 4 (potassium permanganate) are thrown into water, they will give it a beautiful crimson color within a few minutes. However, if you sprinkle KMnO 4 crystals on a piece of ice and put it all in the freezer, after several hours the potassium permanganate will not be able to fully color the frozen H 2 O.

From the previous example we can draw another conclusion about the conditions of diffusion. In addition to the state of aggregation, temperature also affects the rate of interpenetration of particles.

To consider the dependence of the process under consideration on it, it is worth learning about such a concept as the diffusion coefficient. This is the name of the quantitative characteristic of its speed.

In most formulas it is denoted using the capital Latin letter D and in the SI system it is measured in square meters per second (m²/s), sometimes in centimeters per second (cm 2 /m).

The diffusion coefficient is equal to the amount of substance scattered through a unit surface over a unit of time, provided that the difference in densities on both surfaces (located at a distance equal to a unit length) is equal to unity. The criteria that determine D are the properties of the substance in which the process of particle dispersion itself occurs, and their type.

The dependence of the coefficient on temperature can be described using the Arrhenius equation: D = D 0exp (-E/TR).

In the considered formula, E is the minimum energy required to activate the process; T - temperature (measured in Kelvin, not Celsius); R is the gas constant, characteristic of an ideal gas.

In addition to all of the above, the rate of diffusion in solids and liquids in gases is affected by pressure and radiation (induction or high-frequency). In addition, much depends on the presence of a catalytic substance; often it acts as a trigger for the active dispersion of particles.

Diffusion equation

This phenomenon is private view partial differential equations.

Its goal is to find the dependence of the concentration of a substance on the size and coordinates of space (in which it diffuses), as well as time. In this case, the given coefficient characterizes the permeability of the medium for the reaction.

Most often, the diffusion equation is written as follows: ∂φ (r,t)/∂t = ∇ x.

In it, φ (t and r) is the density of the scattering matter at point r at time t. D (φ, r) is the generalized diffusion coefficient at density φ at point r.

∇ is a vector differential operator whose coordinate components are partial derivatives.

When the diffusion coefficient is density dependent, the equation is nonlinear. When not - linear.

Having considered the definition of diffusion and features this process in different environments, it can be noted that it has both positive and negative sides.