Dynamic change is built into nature itself. Everything changes one way or another every moment. If you look around carefully, you will find hundreds of examples of physical and chemical phenomena that are quite natural transformations.
Change is the only constant in the universe
Ironically, change is the only constant in our universe. In order to understand physical and chemical phenomena (examples in nature are found at every step), it is customary to classify them according to types, depending on the nature of the end result caused by them. Distinguish between physical, chemical and mixed changes, which contain both the first and the second.
Physical and chemical phenomena: examples and meaning
What is a physical phenomenon? Any changes that occur in a substance without changing its chemical composition are physical. They are characterized by changes in physical attributes and material state (solid, liquid or gaseous), density, temperature, volume, which occur without changing its fundamental chemical structure. There is no creation of new chemical products or a change in the total mass. In addition, this type of change is usually temporary and in some cases completely reversible.
When you mix chemicals in the laboratory, it is easy to see the reaction, but there are many chemical reactions going on in the world around you every day. A chemical reaction changes molecules, while a physical change only rearranges them. For example, if we take chlorine gas and sodium metal and combine them, we get table salt. The resulting substance is very different from any of its constituent parts. This is a chemical reaction. If we then dissolve this salt in water, we simply mix the salt molecules with the water molecules. There is no change in these particles, it is a physical transformation.
Examples of physical changes
Everything is made of atoms. When atoms join together, different molecules are formed. The different properties that objects inherit are the result of different molecular or atomic structures. The main properties of an object depend on their molecular location. Physical changes occur without changing the molecular or atomic structure of objects. They simply transform the state of the object without changing its nature. Melting, condensation, volume change and evaporation are examples of physical phenomena.
Additional examples of physical changes: metal expanding when heated, sound transmission through air, water freezing into ice in winter, copper is drawn into wires, clay forming on different objects, ice cream melts to liquid, metal heating and transforming it into another form, iodine sublimation when heating, falling of any object by gravity, ink absorbed by chalk, magnetizing iron nails, snowman melting in the sun, glowing incandescent bulbs, magnetic levitation of an object.
How to distinguish between physical and chemical changes?
Many examples of chemical and physical phenomena can be found in life. It is often difficult to tell the difference between the two, especially when both can happen at the same time. To identify physical changes, ask the following questions:
- Is the state of the state of an object a change (gaseous, solid, and liquid)?
- Is the change a purely limited physical parameter or characteristic such as density, shape, temperature, or volume?
- Is the chemical nature of the object a change?
- Do chemical reactions occur that lead to the creation of new products?
If the answer to one of the first two questions is yes, and there are no answers to the following questions, it is most likely a physical phenomenon. Conversely, if the answer to either of the last two questions is yes, while the first two are negative, it is definitely a chemical phenomenon. The trick is to just clearly observe and analyze what you see.
Examples of chemical reactions in everyday life
Chemistry takes place in the world around you, not just in the laboratory. Matter interacts to form new products through a process called chemical reaction or chemical change. Every time you cook or clean, this is chemistry at work. Your body lives and grows through chemical reactions. There are reactions when you are on medication, light a match, and sigh. Here are 10 chemical reactions in everyday life. This is just a small selection of the physical and chemical phenomena in life that you see and experience many times every day:
- Photosynthesis. Chlorophyll in plant leaves converts carbon dioxide and water into glucose and oxygen. This is one of the most common daily chemical reactions, and also one of the most important because this is how plants produce food for themselves and animals and convert carbon dioxide into oxygen.
- Aerobic cellular respiration is a reaction with oxygen in human cells. Aerobic cellular respiration is the opposite process of photosynthesis. The difference is that energy molecules combine with the oxygen we breathe to release the energy our cells need, as well as carbon dioxide and water. The energy used by cells is chemical energy in the form of ATP.
- Anaerobic breathing. Anaerobic respiration produces wine and other fermented foods. Your muscle cells perform anaerobic respiration when you deplete your oxygen supply, such as during intense or prolonged exercise. Anaerobic respiration by yeast and bacteria is used for fermentation to produce ethanol, carbon dioxide, and other chemicals that make cheese, wine, beer, yogurt, bread, and many other common foods.
- Combustion is a type of chemical reaction. It is a chemical reaction in everyday life. Every time you light a match or candle, light a fire, you see the combustion reaction. Combustion combines energy molecules with oxygen to produce carbon dioxide and water.
- Rust is a common chemical reaction. Over time, the iron develops a red, flaky coating called rust. This is an example of an oxidation reaction. Other everyday examples include copper verdigers and silver tarnishing.
- Mixing chemicals causes chemical reactions. Baking powder and baking soda perform similar functions in baking, but they react differently to other ingredients, so you can't always substitute for another. If you combine vinegar and baking soda for chemical "volcano" or milk with baking powder in a recipe, you are experiencing a double-shift or metathesis reaction (plus a few others). The ingredients are recombined to produce carbon dioxide gas and water. Carbon dioxide forms bubbles and helps "grow" baked goods. These reactions seem simple in practice, but often involve several steps.
- Batteries are examples of electrochemistry. Batteries use electrochemical or redox reactions to convert chemical energy into electrical energy.
- Digestion. Thousands of chemical reactions take place during digestion. Once you put food in your mouth, an enzyme in your saliva called amylase begins to break down sugars and other carbohydrates into simpler forms that your body can absorb. The hydrochloric acid in your stomach reacts with food to break it down, and enzymes break down proteins and fats so they can be absorbed into the bloodstream through the intestinal wall.
- Acid-base reactions. Whenever you mix an acid (eg vinegar, lemon juice, sulfuric acid, hydrochloric acid) with an alkali (eg baking soda, soap, ammonia, acetone), you are performing an acid-base reaction. These processes neutralize each other, producing salt and water. Sodium chloride is not the only salt that can be formed. For example, here is the chemical equation for an acid-base reaction that produces potassium chloride, a common table salt substitute: HCl + KOH → KCl + H 2 O.
- Soap and detergents. They are purified by chemical reactions. Soap emulsifies dirt, which means oil stains bind to the soap so they can be removed with water. Detergents reduce the surface tension of the water, so they can interact with oils, isolate them and rinse them out.
- Chemical reactions during cooking. Cooking is one great practical experiment in chemistry. Cooking uses heat to induce chemical changes in food. For example, when you boil an egg vigorously, the hydrogen sulfide produced by heating the egg white can react with the iron in the egg yolk to form a gray-green ring around the yolk. When you cook meats or baked goods, the Maillard reaction between amino acids and sugars gives the brown color and the desired flavor.
Other examples of chemical and physical phenomena
Physical properties describe characteristics that do not change a substance. For example, you can change the color of the paper, but it is still paper. You can boil water, but when you collect and condense steam, it is still water. You can determine the mass of a sheet of paper and it is still paper.
Chemical properties are those that indicate how a substance reacts or does not react with other substances. When sodium metal is placed in water, it reacts violently to form sodium hydroxide and hydrogen. Sufficient heat is generated by the hydrogen bursting into flames, reacting with the oxygen in the air. On the other hand, when you put a piece of copper metal in water, there is no reaction. Thus, the chemical property of sodium is that it reacts with water, while the chemical property of copper is that it does not.
What other examples of chemical and physical phenomena can be cited? Chemical reactions always take place between electrons in the valence shells of the atoms of the elements in the periodic table. Physical phenomena at low energy levels simply involve mechanical interactions - random collisions of atoms without chemical reactions such as atoms or gas molecules. When the collision energies are very high, the integrity of the atomic nucleus is disrupted, resulting in the fission or fusion of the species involved. Spontaneous radioactive decay is usually considered a physical phenomenon.
Man lives in the natural world. You yourself and everything that surrounds you - air, trees, river, sun - these are different objects of nature... Changes constantly occur to objects of nature, which are called natural phenomena.
Since ancient times, people have tried to understand: how and why various phenomena occur? How do birds fly and why don't they fall? How can a tree float on water and why doesn't it sink? Some natural phenomena - thunder and lightning, solar and lunar eclipses - frightened people until scientists figured out how and why they occur.
Observing and studying the phenomena occurring in nature, people have found their application in their lives. Observing the flight of birds (Fig. 1), people constructed an airplane (Fig. 2).
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Observing a floating tree, man learned to build ships, conquered the seas and oceans. Having studied the way the jellyfish travels (Fig. 3), scientists came up with a rocket engine (Fig. 4). By observing lightning, scientists discovered electricity, without which people today cannot live and work. All kinds of household electrical devices (lighting lamps, televisions, vacuum cleaners) surround us everywhere. Various electrical tools (electric drill, electric saw, sewing machine) are used in school workshops and in production.
Scientists have divided all physical phenomena into groups (Fig. 6):
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Mechanical phenomena- these are phenomena that occur with physical bodies when they move relative to each other (rotation of the Earth around the Sun, movement of cars, swing of a pendulum).
Electrical phenomena- these are the phenomena that arise when the appearance, existence, movement and interaction of electric charges (electric current, lightning).
Magnetic phenomena- these are phenomena associated with the appearance of magnetic properties in physical bodies (the attraction of iron objects by a magnet, the rotation of the compass needle to the north).
Optical phenomena- these are phenomena that occur during the propagation, refraction and reflection of light (reflection of light from a mirror, mirages, the appearance of a shadow).
Thermal phenomena- these are the phenomena associated with the heating and cooling of physical bodies (boiling of a kettle, the formation of fog, the transformation of water into ice).
Atomic phenomena- these are phenomena that arise when the internal structure of the substance of physical bodies changes (glow of the Sun and stars, atomic explosion).
Observe and explain. 1. Give an example of a natural phenomenon. 2. What group of physical phenomena does it belong to? Why? 3. Name the physical bodies that participated in physical phenomena.
We are surrounded by an endlessly diverse world of substances and phenomena.
It is constantly changing.
Any changes that occur to bodies are called phenomena. The birth of stars, the change of day and night, the melting of ice, the swelling of buds on trees, the flashing of lightning during a thunderstorm, and so on - all these are natural phenomena.
Physical phenomena
Let's remember that bodies are made of substances. Note that in some phenomena the substances of the bodies do not change, while in others they do. For example, if you tear a piece of paper in half, then, despite the changes that have occurred, the paper remains paper. If the paper is burned, it will turn into ash and smoke.
Phenomena in which the size, shape of bodies, the state of substances can change, but substances remain the same, do not turn into others, are called physical phenomena(evaporation of water, the glow of an electric bulb, the sound of the strings of a musical instrument, etc.).
Physical phenomena are extremely varied. Among them there are mechanical, thermal, electrical, light and etc.
Let's remember how clouds float across the sky, an airplane flies, a car rides, an apple falls, a trolley rolls, etc. In all these phenomena, objects (bodies) move. The phenomena associated with a change in the position of a body in relation to other bodies are called mechanical(translated from Greek "mehane" means machine, tool).
Many phenomena are caused by changes in heat and cold. In this case, changes in the properties of the bodies themselves occur. They change shape, size, the state of these bodies changes. For example, when heated, ice turns into water, water - into steam; when the temperature drops, steam turns into water, water - into ice. The phenomena associated with the heating and cooling of bodies are called thermal(fig. 35).
Rice. 35. Physical phenomenon: the transition of a substance from one state to another. If you freeze water droplets, ice will reappear
Consider electrical phenomena. The word "electricity" comes from the Greek word for "electron" - amber. Recall that when you quickly take off your wool sweater, you hear a slight crackling sound. If you do the same in total darkness, you will also see sparks. This is the simplest electrical phenomenon.
To get acquainted with another electrical phenomenon, do the following experiment.
Pick up small pieces of paper and place them on the table top. Comb through clean, dry hair with a plastic comb and bring it up to the pieces of paper. What happened?
Rice. 36. Small pieces of paper are attracted to the comb
Bodies that, after rubbing, are capable of attracting light objects are called electrified(fig. 36). Lightning in thunderstorms, auroras, electrification of paper and synthetic fabrics are all electrical phenomena. The operation of a telephone, radio, television, and various household appliances are examples of human use of electrical phenomena.
The phenomena that are associated with light are called light. Light is emitted by the Sun, stars, lamps and some living things, such as firefly beetles. Such bodies are called luminous.
We see under the condition of exposure to light on the retina of the eye. We cannot see in absolute darkness. Objects that do not emit light themselves (for example, trees, grass, pages of this book, etc.) are visible only when they receive light from some luminous body and reflect it from their surface.
The moon, which we often speak of as a night light, is in reality only a kind of reflector of sunlight.
Studying the physical phenomena of nature, man learned to use them in everyday life, everyday life.
1. What are called natural phenomena?
2. Read the text. List what natural phenomena are called in it: “Spring has come. The sun is getting warmer. The snow is melting, streams are running. On the trees buds swelled, rooks flew in. "
3. What phenomena are called physical?
4. From the physical phenomena listed below, write down the mechanical phenomena in the first column; in the second - thermal; in the third - electric; in the fourth, light phenomena.
Physical phenomena: flash of lightning; snow melting; coast; melting of metals; work of an electric bell; rainbow in the sky; sunny bunny; moving stones, sand with water; boiling water.
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Physical bodies are the "actors" of physical phenomena. Let's get acquainted with some of them.
Mechanical phenomena
Mechanical phenomena are the movement of bodies (Fig. 1.3) and their action on each other, for example, repulsion or attraction. The action of bodies on each other is called interaction.
We will get acquainted with mechanical phenomena in more detail this academic year.
Rice. 1.3. Examples of mechanical phenomena: movement and interaction of bodies during sports competitions (a, b, c); the movement of the Earth around the Sun and its rotation around its own axis (r)
Sound phenomena
Sound phenomena, as the name suggests, are phenomena associated with sound. These include, for example, the propagation of sound in air or water, as well as the reflection of sound from various obstacles, such as mountains or buildings. When sound is reflected, an echo familiar to many arises.
Thermal phenomena
Thermal phenomena are the heating and cooling of bodies, as well as, for example, evaporation (the transformation of a liquid into vapor) and melting (the transformation of a solid into a liquid).
Thermal phenomena are extremely widespread: for example, they cause the water cycle in nature (Fig. 1.4).
Rice. 1.4. The water cycle in nature
Warmed by the sun's rays, the water of the oceans and seas evaporates. As the steam rises, it cools down, turning into water droplets or ice crystals. They form clouds, from which water returns to Earth in the form of rain or snow.
The real "laboratory" of thermal phenomena is the kitchen: whether soup is boiled on the stove, water is boiling in a kettle, whether food is frozen in the refrigerator - all these are examples of thermal phenomena.
The operation of a car engine is also caused by thermal phenomena: when gasoline burns, a very hot gas is formed, which pushes the piston (engine part). And the movement of the piston is transmitted through special mechanisms to the wheels of the car.
Electrical and magnetic phenomena
The most striking (in the literal sense of the word) example of an electrical phenomenon is lightning (Fig. 1.5, a). Electric lighting and electric transport (Fig. 1.5, b) became possible due to the use of electrical phenomena. Examples of magnetic phenomena are the attraction of iron and steel objects by permanent magnets, and the interaction of permanent magnets.
Rice. 1.5. Electrical and magnetic phenomena and their uses
The compass needle (Fig. 1.5, c) turns so that its "north" end points to the north precisely because the arrow is a small permanent magnet, and the Earth is a huge magnet. The northern lights (Fig. 1.5, d) are caused by the fact that electrically charged particles flying from space interact with the Earth as with a magnet. Electrical and magnetic phenomena cause the operation of televisions and computers (Fig. 1.5, e, f).
Optical phenomena
Wherever we look, we will see optical phenomena everywhere (Fig. 1.6). These are phenomena associated with light.
An example of an optical phenomenon is the reflection of light by various objects. The rays of light reflected by objects fall into our eyes, due to which we see these objects.
Rice. 1.6. Examples of optical phenomena: The sun emits light (s); The moon reflects sunlight (b); mirrors reflect light especially well (c); one of the most beautiful optical phenomena - rainbow (g)