Diffusion in solid liquid and gaseous substances. Diffusion

Absolutely all people have heard about such a concept as diffusion. This was one of the topics in 7th grade physics lessons. Despite the fact that this phenomenon surrounds us absolutely everywhere, few people know about it. What does it mean anyway? What is its physical meaning And how can you make life easier with it? Today we will talk about this.

Diffusion in physics: definition

This is the process of penetration of molecules of one substance between the molecules of another substance. talking plain language, this process can be called mixing. During this mixing occurs the mutual penetration of the molecules of a substance between each other. For example, when making coffee, the molecules instant coffee penetrate water molecules and vice versa.

The speed of this physical process depends on the following factors:

Temperature.
Aggregate state of matter.
External influence.

The higher the temperature of a substance, the faster the molecules move. Hence, mixing process occurs faster at higher temperatures.

Aggregate state of matter - the most important factor . In each state of aggregation, the molecules move at a certain speed.

Diffusion can proceed in the following states of aggregation:

Liquid.
Solid.

Most likely, the reader will now have the following questions:

What are the causes of diffusion?
Where does it flow faster?
How is it applied in real life?

The answers to them can be found below.

Causes

Absolutely everything in this world has its own reason. And diffusion is no exception. Physicists are well aware of the reasons for its occurrence. How to bring them to ordinary person?

Surely everyone has heard that molecules are in constant motion. Moreover, this movement is disorderly and chaotic, and its speed is very high. Thanks to this movement and the constant collision of molecules, their mutual penetration occurs.

Is there any evidence for this movement? Certainly! Remember how quickly you started to smell perfume or deodorant? And the smell of the food your mom cooks in the kitchen? Remember how fast preparing tea or coffee. All this could not be, if not for the movement of molecules. We conclude that the main reason for diffusion is the constant movement of molecules.

Now only one question remains - what is the reason for this movement? It is driven by the desire for balance. That is, in the substance there are areas with high and low concentrations of these particles. And because of this desire, they are constantly moving from an area of high concentration to a low concentration. They are constantly collide with each other, and interpenetration occurs.

Diffusion in gases

The process of mixing particles in gases is the fastest. It can occur both between homogeneous gases and between gases with different concentrations.

Vivid examples from life:

You smell the air freshener through diffusion.
You smell the cooked food. Note that you begin to feel it immediately, and the smell of the freshener after a few seconds. This is due to the fact that at high temperatures the speed of movement of molecules is greater.
Tears that arise when you cut onions. Onion molecules mix with air molecules, and your eyes react to this.

How does diffusion occur in liquids?

Diffusion in liquids proceeds more slowly. It can last from several minutes to several hours.

The brightest examples from life:

Preparation of tea or coffee.
Mixing water and potassium permanganate.
Preparing a solution of salt or soda.

In these cases, diffusion proceeds very quickly (up to 10 minutes). However, if an external influence is applied to the process, for example, stirring these solutions with a spoon, then the process will go much faster and take no more than one minute.

Diffusion when mixing thicker liquids will take much longer. For example, mixing two liquid metals can take several hours. Of course, you can do this in a few minutes, but in this case it will turn out poor quality alloy.

For example, diffusion when mixing mayonnaise and sour cream will take a very long time. However, if you resort to the help of external influence, then this process will not take even a minute.

Diffusion in solids: examples

In solids, the mutual penetration of particles proceeds very slowly. This process may take several years. Its duration depends on the composition of the substance and its structure. crystal lattice.

Experiments proving that diffusion in solids exists.

Sticking of two plates of different metals. If you keep these two plates close to each other and under pressure, within five years there will be a layer between them having a width of 1 millimeter. This small layer will contain molecules of both metals. These two plates will be merged together.
A very thin lead cylinder is applied to a very thin layer gold. After that, this design is placed in an oven for 10 days. The air temperature in the furnace is 200 degrees Celsius. After this cylinder was cut into thin disks, it was very clearly seen that the lead penetrated into the gold and vice versa.

Examples of diffusion in the surrounding world

As you already understood, the harder the medium, the lower the rate of mixing of molecules. Now let's talk about where in real life you can get practical benefits from this physical phenomenon.

The process of diffusion occurs in our life all the time. Even when we lie on the bed, a very thin layer of our skin remains on the surface of the sheet. It also absorbs sweat. It is because of this that the bed becomes dirty and needs to be changed.

So, the manifestation of this process in everyday life can be as follows:

When spreading butter on bread, it is absorbed into it.
When pickling cucumbers, salt first diffuses with water, after which salty water begins to diffuse with cucumbers. As a result, we get delicious snack. Banks need to be rolled up. This is necessary so that the water does not evaporate. More precisely, water molecules should not diffuse with air molecules.
When washing dishes, the molecules of water and detergent penetrate the molecules of the remaining pieces of food. This helps them come off the plate and make it cleaner.

Manifestation of diffusion in nature:

The process of fertilization occurs precisely due to this physical phenomenon. The molecules of the egg and sperm diffuse, after which the embryo appears.
Soil fertilization. Through the use of certain chemicals or compost makes the soil more fertile. Why is this happening? The bottom line is that fertilizer molecules diffuse with soil molecules. After that, the diffusion process occurs between the molecules of the soil and the root of the plant. Thanks to this, the season will be more fruitful.
Mixing industrial waste with air greatly pollutes it. Because of this, within a radius of a kilometer, the air becomes very dirty. Its molecules diffuse with molecules clean air from neighboring areas. This is how the ecological situation in the city worsens.

The manifestation of this process in industry:

Siliconization is a process of diffusion saturation with silicon. It is carried out in a gaseous atmosphere. The silicon-saturated layer of the part has not very high hardness, but high corrosion resistance and increased wear resistance in sea water, nitric, hydrochloric in sulfuric acids.
Diffusion in metals plays an important role in the production of alloys. To obtain a high-quality alloy, it is necessary to produce alloys at high temperatures and with external influence. This will greatly speed up the diffusion process.

These processes occur in various industries:

Electronic.
Semiconductor.
Engineering.

As you understand, the process of diffusion can have both positive and negative effects on our lives. You need to be able to manage your life and maximize the benefits of this physical phenomenon, as well as minimize harm.

Now you know what is the essence of such a physical phenomenon as diffusion. It consists in the mutual penetration of particles due to their movement. Everything in life moves. If you are a student, then after reading our article you will definitely get a grade of 5. Good luck to you!

Have you ever seen hordes of small annoying midges randomly swarming overhead? Sometimes it seems that they seem to be hanging motionless in the air. On the one hand, this swarm is motionless, on the other, the insects inside it are constantly moving right, then left, then up, then down, constantly colliding with each other and scattering again within this cloud, as if an invisible force holds them together.

The movements of molecules are of a similar chaotic nature, while the body retains a stable shape. This movement is called the thermal motion of molecules.

Brownian motion

Back in 1827, the famous British botanist Robert Brown used a microscope to study the behavior of microscopic pollen particles in water. He drew attention to the fact that the particles constantly moved in a chaotic, defying logical order, and this random movement did not depend either on the movement of the liquid in which they were located, or on its evaporation. The smallest particles of pollen described complex, mysterious trajectories. Interestingly, the intensity of such movement does not decrease with time and is not related to chemical properties medium, but only increases if the viscosity of this medium or the size of moving particles decreases. In addition, temperature has a great influence on the speed of movement of molecules: the higher it is, the faster the particles move.

Diffusion

A long time ago, people realized that all substances in the world consist of the smallest particles: ions, atoms, molecules, and there are gaps between them, and these particles are constantly and randomly moving.

Consequence thermal motion molecules is diffusion. We can see examples almost everywhere in Everyday life: both in everyday life and in wildlife. This is the spread of odors, gluing various solid objects, mixing liquids.

talking scientific language, diffusion is the phenomenon of the penetration of molecules of one substance into the gaps between the molecules of another substance.

Gases and diffusion

The simplest example of diffusion in gases is the fairly rapid spread of odors (both pleasant and not so pleasant) in the air.

Diffusion in gases can be extremely dangerous, because of this phenomenon poisoning with carbon monoxide and other toxic gases proceeds at lightning speed.

If diffusion in gases occurs quickly, most often in a matter of seconds, then diffusion in liquids takes whole minutes and sometimes even hours. It depends on density and temperature.

One example is the very rapid dissolution of salts, alcohols and acids, a short time forming homogeneous solutions.

Diffusion in solids

AT solids diffusion is the most difficult, at normal room or street temperature it is invisible. In all modern and old school textbooks, the experiment with lead and gold plates is described as an example. This experiment showed that only after more than four years, a negligible amount of gold penetrated into lead, and lead penetrated into gold to a depth of no more than five millimeters. This difference is due to the fact that the density of lead is much higher than the density of gold.

Consequently, the speed and intensity of diffusion depends not least on the density of the substance and the speed of the chaotic movement of molecules, and the speed, in turn, depends on temperature. Diffusion proceeds more intensively and faster at higher temperatures.

Examples of diffusion in everyday life

We do not even think about the fact that every day at almost every step we encounter the phenomenon of diffusion. That is why this phenomenon is considered one of the most significant and interesting in physics.

One of the simplest examples of diffusion in everyday life is the dissolution of sugar in tea or coffee. If a piece of sugar is placed in a glass of boiling water, after a while it will disappear without a trace, while even the volume of the liquid will practically not change.

If you look around carefully, you can find many examples of diffusion that make our life easier:

dissolution washing powder, potassium permanganate, salt;
spraying air fresheners;
aerosols for the throat;
washing away dirt from the surface of the linen;
mixing colors by the artist;
dough kneading;
cooking rich broths, soups, and gravy, sweet compotes and fruit drinks.

In 1638, returning from Mongolia, Ambassador Vasily Starkov presented the Russian Tsar Mikhail Fedorovich as a gift with almost 66 kg of dried leaves with a strange pungent aroma. Muscovites who have never tried it liked this dried plant very much, and they still use it with pleasure. Did you recognize him? Of course, this is tea that is brewed due to the phenomenon of diffusion.

Examples of diffusion in the surrounding world

The role of diffusion in the world around us is very great. One of the most important examples of diffusion is the blood circulation in living organisms. Oxygen from the air enters the blood capillaries located in the lungs, then dissolves in them and spreads throughout the body. In turn, carbon dioxide diffuses from the capillaries into the alveoli of the lungs. Nutrients released from food by diffusion penetrate into the cells.

In herbaceous plant species, diffusion occurs through their entire green surface, in larger flowering plants- through leaves and stems, in shrubs and trees - through cracks in the bark of trunks and branches and lentils.

In addition, an example of diffusion in the surrounding world is the absorption of water and minerals dissolved in it by the root system of plants from the soil.

It is diffusion that is the reason why the composition of the lower layer of the atmosphere is heterogeneous and consists of several gases.

Unfortunately, in our imperfect world, there are very few people who do not know what an injection, also known as an "injection", is. This kind of painful but effective treatment also based on the phenomenon of diffusion.

Pollution environment: soil, air, water bodies - these are also examples of diffusion in nature.

Melting white clouds in the blue sky, so beloved by poets of all times - she is also a diffusion known to every student of middle and high school!

So, diffusion is something without which our life would not only be more difficult, but almost impossible.

Physics teacher Nozdrina L.D.

Diffusion in gases, liquids and solids.

slide 2

Goals and objectives of the lesson

Basic provisions of the ICB;

Definition of diffusion;

Features of the diffusion process in various media.

Explain the phenomenon of diffusion on the basis of MKT.

slide 3

A molecule is the smallest particle of a substance.
Mikhail Vasilyevich Lomonosov in 1745 distinguished between the concepts of atom and molecule.
Molecules are made up of atoms.
An atom is the smallest particle of a chemical element.

slide 4

Three states of matter

The size of the molecule is about 10‾¹ºm

Let's repeat

slide 5

"I put one experience above 1000 opinions born of the imagination"

M. V. Lomonosov

Sources of physical knowledge

slide 6

Brownian motion

Robert Brown in 1827, observing a suspension in the form of plant pollen under a microscope, discovered that the particles are in continuous motion, describing complex trajectories.

Slide 8

Diffusion observed

In gases
in liquids
In solids

Slide 9

Aroma oils, resins are widely used in the perfume industry, therapeutic aromatherapy, for church needs.

Diffusion of gases in gases

Slide 10

Diffusion of gases in gases

aromatic substances
Oils
resins
jasmine petals
Rose petals
Myrrh
incense tree

slide 11

Who among us has not been struck by the smell of a spring night? We could smell the smells of bird cherry, acacia, lilac. Molecules of the smelling substance of flowers diffuse into the air.

Diffusion of gases in gases

slide 12

Tea, coffee and cocoa are commonly used as tonic cultures.

The birthplace of tea is China, coffee is Africa, cocoa is America. The rapid spread of the aroma of these drinks is explained by the fact that the molecules of the odorous substance penetrate between the molecules of the air.

Diffusion of gases in gases

slide 13

The most numerous way insects communicate is through olfactory chemicals, which animals use to protect themselves or attract attention.

The transfer of odors is carried out by diffusion.

Diffusion of gases in gases

Slide 14

Attractive
Pheromones, hormones.
Diffusion of gases in gases
Fragrances
butterflies
Maybugs
ferrets
bedbugs
Skunks
repulsive
Repellents

slide 15

Forests are the lungs of the planet, helping to breathe for all living things.

City air contains a lot of gaseous substances ( carbon monoxide, carbon dioxide, nitrogen oxides, sulfur) obtained as a result of the work of the industrial complex, transport and public utilities.

The process of air purification by the forest can be explained by diffusion.

Diffusion of gases in gases

slide 16

Natural combustible gas is colorless and odorless.

Diffusion of gases in gases

Due to diffusion, the gas spreads throughout the room, forming an explosive mixture.

Slide 18

Solutions environmental problem associated with air purification:

1) filters on the exhaust pipes;

2) growing plants along roads and around enterprises that absorb harmful substances.

Diffusion of gases in gases

Poplar

Slide 19

Observation of the process of diffusion of air molecules and molecules ammonia(the indicator is litmus test, fixing the presence of an alkaline environment)

OUR EXPERIMENT

Slide 20

Observation of the dissolution of smoke from a fire in the air.

OUR EXPERIMENT

slide 21

OUR EXPERIMENT

Spreading the smell of the air freshener in the room.

slide 22

Bee venom is a colorless transparent liquid with a fragrant odor and high biological activity.

The rapid penetration of bee venom is associated with biological processes in the body

(with the movement of poison molecules and their interaction with the intercellular fluid of the connective tissue).

DIFFUSION OF LIQUID IN LIQUID

slide 23

For making tea, flowers and leaves of some plants are used: jasmine, rose, linden, oregano, mint, thyme and others.

DIFFUSION OF LIQUID IN LIQUID

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DIFFUSION OF LIQUID IN LIQUID

Green
Black

In the solid state, the color of the tea depends on how the leaves are processed.

Tea brewing is based on the diffusion of water molecules and the coloring matter of plants.

Slide 25

OUR EXPERIMENT

We invite you for tea.

slide 26

OUR EXPERIMENT

Comparison of the rate of diffusion when brewing tea cold and hot water.

The diffusion process accelerates with increasing temperature; occurs more slowly than in gases.

Slide 27

Adding a slice of lemon makes the tea lighter.

OUR EXPERIMENT

The color of tea is brown only in a neutral environment (in water).

Slide 28

OUR EXPERIMENT

To saturate the color of the beets, acetic acid is added to the water.

Slide 29

The smell of salt, the smell of iodine.

Unassailable and proud

Reefs stone muzzles

Getting out of the water...

Y. Drunina

Every year 2 billion tons of salts enter the atmosphere.

slide 30

Smog is a yellow mist that poisons the air we breathe.

Smog is the main cause of respiratory and heart diseases, weakening of human immunity.

DIFFUSION OF A SOLID STATE IN GASES

Slide 31

DIFFUSION OF A SOLID STATE IN GASES

Particles found in urban air.

plant pollen
Microorganisms and their spores
dry sand
coal dust
cement dust
Fertilizer
Asbestos
Cadmium
Mercury
Lead
iron oxide
copper oxide
Particle radius, µm
20 – 60
1 - 15
200 - 2000
10 – 400
10 – 150
30 – 800
10 – 200
0,5-1
0,1-1
0,1-1

slide 32

How to explain the process of pickling vegetables?

Slide 33

DIFFUSION OF A SOLID IN A LIQUID

Mushroom pickles

slide 34

Fruit pickles

DIFFUSION OF A SOLID IN A LIQUID

During salting, salt crystals decompose into Na and Cl ions in an aqueous solution, move randomly and occupy the gaps between the pores of food products.

Slide 35

Preparing jams and compotes.

DIFFUSION OF A SOLID IN A LIQUID

slide 36

Obtaining sugar from beets in industrial production

DIFFUSION OF A SOLID IN A LIQUID

Slide 37

Dissolution of potassium permanganate crystals in water.

OUR EXPERIMENT

Slide 38

OUR EXPERIMENT

Dissolving sugar crystals in hot water.

Slide 39

Dissolution of the tablet "Mukaltin" in water.

OUR EXPERIMENT

Slide 40

Cooking pickles, sauerkraut, salted fish and lard at home.

OUR EXPERIMENT

Slide 41

To impart hardness, wear resistance and tensile strength to iron and steel parts, their surfaces are subjected to diffuse saturation with carbon (cementation)

Slide 42

The English metallurgist William Roberts-Austin measured the diffusion of gold in lead by placing this cylinder in a furnace at about 200°C for 10 days.

The gold atoms were evenly distributed over the entire lead cylinder.

slide 43

OUR EXPERIMENT

Observation of the phenomenon of diffusion of potassium permanganate and wax molecules.

Slide 44

OUR EXPERIMENT

Result in three weeks.
Two months have passed.
Molecules in solids diffuse the slowest.

Slide 45

The cause of diffusion is the random movement of molecules.
The rate of diffusion depends on the state of aggregation of the contacting bodies.
Diffusion is fast in gases, slower in liquids, and very slow in solids.
The diffusion process accelerates with an increase in temperature, with a decrease in the viscosity of the medium and particle size.

Slide 46

1. Which figure most correctly shows a drop of water in a microscope at high magnification?

2. Having models of particles of two substances, show what happens in a substance when they mix spontaneously.

3. Choose a picture in which the direction of the arrows correctly indicates the direction of movement of two particles in the substance.

Describe how particles move in matter.

What dances or melodies can be compared with the movement of particles of a palm tree growing in Africa, and particles of a cedar growing in Siberia?

Slide 47

Everyone knows how useful onion. But when we cut it, we shed tears. Explain why?

This is due to the phenomenon of diffusion. The reason is the volatile substance lachrymator, which causes tears. It dissolves in the fluid of the mucous membrane of the eye, releasing sulfuric acid which irritates the mucous membrane of the eye.

Slide 48

Middle level: 1. In which brine - hot or cold - cucumbers pickle faster?

2. Why can't a fabric dyed with low-quality paint be kept wet in contact with light-colored linen?

Sufficient level: 1. Why does the smoke from the fire, rising up, quickly cease to be visible even in calm weather?

2. Will odors spread in a hermetically sealed basement where there are absolutely no drafts?

High level: 1. An open vessel with ether was balanced on the scales and left alone. After some time, the balance of the scales was disturbed. Why?

2. What is the importance of diffusion for the processes of respiration in humans and animals?

Slide 49

1. Paragraph No. 9, questions for the paragraph;

2. Experimental task (describe the diffusion phenomena observed at home).

3. Answer the question in writing:

Why does sweet syrup acquire a fruity flavor over time? (middle level)

Why does salted herring become less salty after being left in water for a while? (enough level)

Why is liquid glue and molten solder used in gluing and soldering? ( high level)

Slide 50

Slide 51

1. Semke A.I. "Non-standard problems in physics", Yaroslavl: Academy of Development, 2007.

2. Shustova L.V., Shustov S.B. " Chemical bases ecology. M.: Enlightenment, 1995.

3. Lukashik V.I. Problem book in physics 7-8kl. M.: Education, 2002.

4. Katz Ts.B. Biophysics at physics lessons. M.: Education, 1998.

5. Encyclopedia of Physics. M.: Avanta +, 1999.

6. Bogdanov K.Yu. A physicist visiting a biologist. M.: Nauka, 1986.

7. Enohovich A.S. Handbook of Physics. Moscow: Education, 1990.

8. Olgin O. I. Experiments without explosions. Moscow: Chemistry, 1986.

9. Kovtunovich M.G. "Home experiment in physics grades 7-11." M.: Humanitarian publishing center, 2007.

10. Internet resources.

Literature

View all slides

Numerous experiments show that the molecules of all bodies are in continuous motion. Let's consider one of them.

An aqueous solution is poured into a glass vessel blue vitriol. This solution is dark blue in color and is heavier than water. On top of the solution into the vessel, very carefully so as not to mix the liquids, pour clean water. At the beginning of the experiment, a sharp interface between water and a solution of copper sulphate is visible.

The vessel is left alone and continue to observe the interface of liquids. A few days later, they find that the interface has blurred. After two weeks, the boundary separating one liquid from another disappears, a homogeneous liquid of pale color forms in the vessel. blue color (see color insert I, below). So the liquids are mixed.

The phenomenon in which substances spontaneously mix with each other is called diffusion.

This phenomenon is explained as follows (Fig. 16). First, individual molecules of water and copper sulfate exchange places due to their movement, located near the interface between these liquids. The boundary becomes blurry, since copper sulfate molecules enter the lower layer of water and, conversely, water molecules enter the upper layer copper sulphate solution. Then some of these molecules exchange places with the molecules in the next layers. The interface between liquids becomes even more vague. Since the molecules move continuously and randomly, this process leads to the fact that all the liquid in the vessel becomes homogeneous.

Diffusion occurs faster in gases than in liquids. If some odorous substance, such as naphthalene, is introduced into the room, then very soon its smell will be felt throughout the room. This means that naphthalene molecules penetrate everywhere - diffusion occurs. Naphthalene molecules, colliding with air molecules and moving randomly in all directions, scatter around the room in all directions.

Diffusion also occurs in solids, but very slowly. In one of the experiments, smoothly polished plates of lead and gold were placed one on top of the other and squeezed with a load. With normal room temperature(about 20 ° C) for 5 years, gold and lead have grown together, mutually penetrating each other at a distance of 1 mm. The result was a thin layer of an alloy of gold and lead.

Diffusion has great importance in human and animal life. For example, oxygen from the environment, due to diffusion, penetrates into the body through the human skin. Nutrients through diffusion penetrate from the intestines into the blood of animals.

Diffusion also occurs when soldering metal parts.

Question. one. What is diffusion? Describe an experiment in which the diffusion of liquids is observed. 2. How is diffusion explained from the point of view of the molecular structure of a substance? 3. Under what processes and how does diffusion occur in humans and animals?

An exercise. one. On what phenomenon is the salting of cucumbers, cabbage, fish and other products based? 2. The water of rivers, lakes and other bodies of water always contains molecules of gases that are part of the air. Due to what phenomenon do these molecules get into the water? Why do they penetrate to the bottom of the reservoir? Describe how air is mixed with water. 1 2 3

Exercise. one. Pour into a glass cold water and lower a piece of potassium permanganate to the bottom. Without stirring the water, determine how long it takes for potassium permanganate molecules to enter the top layer of water. Explain the observed phenomenon. 2. Pour equal amounts of water into two glasses. Put one of them in warm place, the other - in the cold (in the refrigerator, out the window, in the canopy). After a while, lower a piece of lead from a “chemical” pencil (or a grain of potassium permanganate) to the bottom of each glass. Put the glasses back in their original places. In the morning and in the evening, mark the position of the border of colored and clear water in these two glasses. Draw the appropriate conclusion based on your experience. 3. Read the paragraph "Brownian motion" at the end of the textbook.

In order for the sugar in the tea to dissolve faster, it must be stirred. But it turns out that if this is not done, then after a while all the sugar will dissolve, and the tea will become sweet. In the course of this lesson, you will learn that such spontaneous mixing of substances is due to the continuous chaotic movement of molecules, and this phenomenon is called diffusion.

Topic: Initial information about the structure of matter

Lesson: Diffusion

In our daily life, we sometimes do not notice some physical phenomena. For example, someone opened a perfume bottle, and we, even being at a great distance, will feel this smell. Climbing the stairs to our apartment, we can smell the food cooked at home. We drop a bag of tea leaves into a glass of hot water, and we don’t even notice how the tea leaves colors all the water in the cup.

Rice. 1. Although the tea leaves are inside the tea bag, they color all the water in the cup.

All of these phenomena are associated with the same physical phenomenon, which is called diffusion. It happens because the molecules of one and the other substance mutually penetrate each other.

Diffusion is the spontaneous mutual penetration of molecules of one substance into the spaces between the molecules of another.

In this definition, every word is important: both spontaneous, and mutual, and penetration, and molecules.

If you pour a solution of copper sulphate (blue) into the vessel, and carefully, without mixing, pour clean water on top, you will notice that at first a fairly clear boundary between water and copper sulphate becomes more and more blurred over time. If the experiment is continued for a week, this boundary will completely disappear, and the liquid in the vessel will become evenly colored.

Rice. 2. Diffusion of a solution of copper sulfate in water

Diffusion in gases occurs much faster. Take a cylindrical glass vessel without a bottom and attach to it inner surface vertical strips of universal indicator paper. These strips have the ability to change their color under the influence of vapors of certain substances. Pour a small amount of such a substance into the bottom of a cup and place a cylindrical vessel in this cup. We will see that at first the indicator strips will change their color in their lower part, but after 10-20 seconds the strips will acquire a bright blue color along their entire length. This means that air and a gaseous substance spontaneously mixed with each other, that is, there was a mutual penetration of the molecules of one substance into the gaps between the molecules of another, which means diffusion has occurred.

Rice. 3. As a result of the diffusion of vapors of a volatile substance, the color of the strips of indicator paper changes first at the bottom, and then along the entire length

It turns out that the rate of diffusion of certain substances can be influenced. To verify this, let's take two glasses, one with hot and the other with cold water. Pour the same amount of instant coffee into both glasses. In one of the glasses, diffusion will go much faster. As it tells you life experience, diffusion occurs the faster, the higher the temperature of the diffusing substances.

Rice. 4. The water in the right glass has a higher temperature, and therefore the diffusion of instant coffee in it is faster

The higher the temperature of the substances, the faster diffusion occurs.

Can diffusion occur in solids? At first glance, no. But experience gives a different answer to this question. If the surfaces of two different metals (for example, lead and gold) are well polished and pressed tightly against each other, then the mutual penetration of metal molecules can be registered to a depth of about one millimeter. True, this will take several years.