Questions about what a state of aggregation is, what features and properties have solids, liquids and gases, are considered in several training courses. There are three classical states of matter, with their own characteristic features of the structure. Their understanding is an important point in comprehending the sciences of the Earth, living organisms, and production activities. These questions are studied by physics, chemistry, geography, geology, physical chemistry and other scientific disciplines. Substances that are under certain conditions in one of the three basic types of state can change with an increase or decrease in temperature or pressure. Consider possible transitions from one state of aggregation to another, as they are carried out in nature, technology and everyday life.
What is the state of aggregation?
The word of Latin origin "aggrego" translated into Russian means "attach". The scientific term refers to the state of the same body, substance. Existence at certain temperature values and different pressures of solids,gases and liquids is characteristic of all shells of the Earth. In addition to the three basic aggregate states, there is also a fourth. At elevated temperature and constant pressure, the gas turns into a plasma. To better understand what a state of aggregation is, it is necessary to remember the smallest particles that make up substances and bodies.
The diagram above shows: a - gas; b - liquid; c is a solid body. In such figures, circles indicate the structural elements of substances. This is a symbol, in fact, atoms, molecules, ions are not solid balls. Atoms consist of a positively charged nucleus around which negatively charged electrons move at high speed. Knowledge of the microscopic structure of matter helps to better understand the differences that exist between different aggregate forms.
Representations of the microcosm: from Ancient Greece to the 17th century
The first information about the particles that make up physical bodies appeared in ancient Greece. Thinkers Democritus and Epicurus introduced such a concept as an atom. They believed that these smallest indivisible particles of different substances have a shape, certain sizes, are capable of movement and interaction with each other. Atomistics became the most advanced teaching of ancient Greece for its time. But its development slowed down in the Middle Ages. Since then scientists were persecuted by the Inquisition of the Roman Catholic Church. Therefore, until modern times, there was no clear concept of what the state of aggregation of matter is. Only after the 17th centuryscientists R. Boyle, M. Lomonosov, D. D alton, A. Lavoisier formulated the provisions of the atomic-molecular theory, which have not lost their significance even today.
Atoms, molecules, ions are microscopic particles of the structure of matter
A significant breakthrough in understanding the microcosm occurred in the 20th century, when the electron microscope was invented. Taking into account the discoveries made by scientists earlier, it was possible to put together a harmonious picture of the microworld. Theories describing the state and behavior of the smallest particles of matter are quite complex; they belong to the field of quantum physics. To understand the features of different aggregate states of matter, it is enough to know the names and features of the main structural particles that form different substances.
- Atoms are chemically indivisible particles. Preserved in chemical reactions, but destroyed in nuclear. Metals and many other substances of atomic structure have a solid state of aggregation under normal conditions.
- Molecules are particles that are broken down and formed in chemical reactions. Molecular structure have oxygen, water, carbon dioxide, sulfur. The aggregate state of oxygen, nitrogen, sulfur dioxide, carbon, oxygen under normal conditions is gaseous.
- Ions are charged particles that atoms and molecules turn into when they gain or lose electrons - microscopic negatively charged particles. Many s alts have an ionic structure, for example, table s alt, iron and copper sulfate.
There are substances whose particles are arranged in a certain way in space. Ordered relative positionatoms, ions, molecules is called a crystal lattice. Usually ionic and atomic crystal lattices are typical for solids, molecular - for liquids and gases. Diamond has a high hardness. Its atomic crystal lattice is formed by carbon atoms. But soft graphite also consists of atoms of this chemical element. Only they are located differently in space. The usual state of aggregation of sulfur is solid, but at high temperatures the substance turns into a liquid and an amorphous mass.
Substances in a solid state of aggregation
Solid bodies under normal conditions retain their volume and shape. For example, a grain of sand, a grain of sugar, s alt, a piece of rock or metal. If sugar is heated, the substance begins to melt, turning into a viscous brown liquid. Stop heating - again we get a solid. This means that one of the main conditions for the transition of a solid into a liquid is its heating or an increase in the internal energy of the particles of a substance. The solid state of aggregation of s alt, which is used in food, can also be changed. But to melt table s alt, you need a higher temperature than when heating sugar. The fact is that sugar consists of molecules, and table s alt consists of charged ions, which are more strongly attracted to each other. Solids in liquid form do not retain their shape because the crystal lattices break down.
The liquid state of aggregation of s alt during melting is explained by the breaking of the bond between ions in crystals. are releasedcharged particles that can carry electrical charges. Molten s alts conduct electricity and are conductors. In the chemical, metallurgical and engineering industries, solids are converted into liquids to obtain new compounds from them or give them different shapes. Metal alloys are widely used. There are several ways to obtain them, associated with changes in the state of aggregation of solid raw materials.
Liquid is one of the basic states of aggregation
If you pour 50 ml of water into a round bottom flask, you will notice that the substance immediately takes the form of a chemical vessel. But as soon as we pour the water out of the flask, the liquid will immediately spread over the surface of the table. The volume of water will remain the same - 50 ml, and its shape will change. These features are characteristic of the liquid form of the existence of matter. Liquids are many organic substances: alcohols, vegetable oils, acids.
Milk is an emulsion, i.e. a liquid in which there are droplets of fat. A useful liquid mineral is oil. It is extracted from wells using drilling rigs on land and in the ocean. Sea water is also a raw material for industry. Its difference from the fresh water of rivers and lakes lies in the content of dissolved substances, mainly s alts. During evaporation from the surface of water bodies, only H2O molecules pass into the vapor state, solutes remain. Methods for obtaining useful substances from sea water and methods for its purification are based on this property.
Whencomplete removal of s alts, distilled water is obtained. It boils at 100°C and freezes at 0°C. The brines boil and turn into ice at different temperatures. For example, water in the Arctic Ocean freezes at a surface temperature of 2°C.
The aggregate state of mercury under normal conditions is a liquid. This silver-gray metal is usually filled with medical thermometers. When heated, the column of mercury rises on the scale, the substance expands. Why do street thermometers use red-tinted alcohol and not mercury? This is explained by the properties of liquid metal. At 30-degree frosts, the aggregate state of mercury changes, the substance becomes solid.
If a medical thermometer breaks and mercury spills out, it is dangerous to pick up silver balls with your hands. It is harmful to inhale mercury vapor, this substance is very toxic. Children in such cases should seek help from their parents, adults.
Gas state
Gases are unable to retain their volume or shape. Fill the flask to the top with oxygen (its chemical formula is O2). As soon as we open the flask, the molecules of the substance will begin to mix with the air in the room. This is due to Brownian motion. Even the ancient Greek scientist Democritus believed that the particles of matter are in constant motion. In solids, under normal conditions, atoms, molecules, ions do not have the opportunity to leave the crystal lattice, to free themselves from bonds with other particles. This is possible only whenlarge amounts of energy from outside.
In liquids, the distance between particles is slightly greater than in solids, they require less energy to break intermolecular bonds. For example, the liquid aggregate state of oxygen is observed only when the gas temperature drops to −183 °C. At −223 °C, O2 molecules form a solid. When the temperature rises above the given values, oxygen turns into a gas. It is in this form that it is under normal conditions. At industrial enterprises, there are special installations for separating atmospheric air and obtaining nitrogen and oxygen from it. First, the air is cooled and liquefied, and then the temperature is gradually increased. Nitrogen and oxygen turn into gases under different conditions.
The Earth's atmosphere contains 21% oxygen and 78% nitrogen by volume. In liquid form, these substances are not found in the gaseous envelope of the planet. Liquid oxygen has a light blue color and is filled at high pressure into cylinders for use in medical facilities. In industry and construction, liquefied gases are necessary for many processes. Oxygen is needed for gas welding and cutting of metals, in chemistry - for the oxidation reactions of inorganic and organic substances. If you open the valve of an oxygen cylinder, the pressure decreases, the liquid turns into a gas.
Liquefied propane, methane and butane are widely used in energy, transport, industry and household activities. These substances are obtained from natural gas or by cracking(splitting) of crude oil. Carbon liquid and gaseous mixtures play an important role in the economy of many countries. But oil and natural gas reserves are severely depleted. According to scientists, this raw material will last for 100-120 years. An alternative source of energy is air flow (wind). Fast-flowing rivers, tides on the shores of the seas and oceans are used to operate power plants.
Oxygen, like other gases, can be in the fourth state of aggregation, representing a plasma. An unusual transition from a solid to a gaseous state is a characteristic feature of crystalline iodine. A dark purple substance undergoes sublimation - turns into a gas, bypassing the liquid state.
How are transitions from one aggregate form of matter to another carried out?
Changes in the aggregate state of substances are not associated with chemical transformations, these are physical phenomena. When the temperature rises, many solids melt and turn into liquids. A further increase in temperature can lead to evaporation, that is, to the gaseous state of the substance. In nature and economy, such transitions are characteristic of one of the main substances on Earth. Ice, liquid, steam are the states of water under different external conditions. The compound is the same, its formula is H2O. At a temperature of 0 ° C and below this value, water crystallizes, that is, it turns into ice. When the temperature rises, the resulting crystals are destroyed - the ice melts, liquid water is again obtained. When it is heated, water vapor is formed. Evaporation -the transformation of water into gas - goes even at low temperatures. For example, frozen puddles gradually disappear because the water evaporates. Even in frosty weather, wet clothes dry out, but this process takes longer than on a hot day.
All the listed transitions of water from one state to another are of great importance for the nature of the Earth. Atmospheric phenomena, climate and weather are associated with the evaporation of water from the surface of the oceans, the transfer of moisture in the form of clouds and fog to land, precipitation (rain, snow, hail). These phenomena form the basis of the World water cycle in nature.
How do the aggregate states of sulfur change?
Under normal conditions, sulfur is bright shiny crystals or a light yellow powder, i.e. it is a solid. The aggregate state of sulfur changes when heated. First, when the temperature rises to 190 ° C, the yellow substance melts, turning into a mobile liquid.
If you quickly pour liquid sulfur into cold water, you get a brown amorphous mass. With further heating of the sulfur melt, it becomes more and more viscous and darkens. At temperatures above 300 ° C, the state of aggregation of sulfur changes again, the substance acquires the properties of a liquid, becomes mobile. These transitions occur due to the ability of the element's atoms to form chains of different lengths.
Why can substances be in different physical states?
The state of aggregation of sulfur - a simple substance - is solid under normal conditions. Sulfur dioxide - gas, sulfuric acid -oily liquid heavier than water. Unlike hydrochloric and nitric acids, it is not volatile; molecules do not evaporate from its surface. What is the state of aggregation of plastic sulfur, which is obtained by heating crystals?
In an amorphous form, the substance has the structure of a liquid, with a slight fluidity. But plastic sulfur simultaneously retains its shape (as a solid). There are liquid crystals that have a number of characteristic properties of solids. Thus, the state of matter under different conditions depends on its nature, temperature, pressure and other external conditions.
What are the features in the structure of solids?
The existing differences between the basic aggregate states of matter are explained by the interaction between atoms, ions and molecules. For example, why does the solid aggregate state of matter lead to the ability of bodies to maintain volume and shape? In the crystal lattice of a metal or s alt, structural particles are attracted to each other. In metals, positively charged ions interact with the so-called "electron gas" - the accumulation of free electrons in a piece of metal. S alt crystals arise due to the attraction of oppositely charged particles - ions. The distance between the above structural units of solids is much smaller than the size of the particles themselves. In this case, electrostatic attraction acts, it gives strength, and repulsion is not strong enough.
To destroy the solid state of aggregation of matter, it is necessarymake an effort. Metals, s alts, atomic crystals melt at very high temperatures. For example, iron becomes liquid at temperatures above 1538 °C. Tungsten is refractory and is used to make incandescent filaments for light bulbs. There are alloys that become liquid at temperatures above 3000 °C. Many rocks and minerals on Earth are in a solid state. This raw material is extracted with the help of equipment in mines and quarries.
To detach even one ion from a crystal, it is necessary to expend a large amount of energy. But after all, it is enough to dissolve s alt in water for the crystal lattice to disintegrate! This phenomenon is explained by the amazing properties of water as a polar solvent. H2O molecules interact with s alt ions, destroying the chemical bond between them. Thus, dissolution is not a simple mixing of different substances, but a physical and chemical interaction between them.
How do the molecules of liquids interact?
Water can be liquid, solid and gas (steam). These are its main states of aggregation under normal conditions. Water molecules are made up of one oxygen atom with two hydrogen atoms bonded to it. There is a polarization of the chemical bond in the molecule, a partial negative charge appears on the oxygen atoms. Hydrogen becomes the positive pole in the molecule and is attracted to the oxygen atom of another molecule. This weak force is called the "hydrogen bond".
Liquid state of aggregation characterizedistances between structural particles comparable with their sizes. The attraction exists, but it is weak, so the water does not retain its shape. Vaporization occurs due to the destruction of bonds, which occurs on the surface of the liquid even at room temperature.
Do intermolecular interactions exist in gases?
The gaseous state of matter differs from liquid and solid in a number of parameters. Between the structural particles of gases there are large gaps, much larger than the size of the molecules. In this case, the forces of attraction do not work at all. The gaseous state of aggregation is characteristic of substances present in the composition of air: nitrogen, oxygen, carbon dioxide. In the picture below, the first cube is filled with a gas, the second with a liquid, and the third with a solid.
Many liquids are volatile, molecules of a substance break off from their surface and pass into the air. For example, if you bring a cotton swab dipped in ammonia to the opening of an open bottle of hydrochloric acid, white smoke appears. Right in the air, a chemical reaction occurs between hydrochloric acid and ammonia, ammonium chloride is obtained. What state of matter is this substance in? Its particles, which form white smoke, are the smallest solid crystals of s alt. This experiment must be carried out under a fume hood, the substances are toxic.
Conclusion
The state of aggregation of gas was studied by many outstanding physicists and chemists: Avogadro, Boyle, Gay-Lussac,Klaiperon, Mendeleev, Le Chatelier. Scientists have formulated laws that explain the behavior of gaseous substances in chemical reactions when external conditions change. The discovered patterns were not only included in school and university textbooks of physics and chemistry. Many chemical industries are based on knowledge about the behavior and properties of substances in different aggregate states.
