What is matter in Chemistry

Introduction to Chemistry – What is Substance

Some basic concepts in chemistry

Chemistry is a scientific and experimental discipline that studies the structure, composition, various changes and properties of matter. The latter, in turn, is defined as “anything that has mass and takes up space”.

Matter can be divided into three states of aggregation: solid, liquid and gas (gas) with the following properties.

What is matter in Chemistry

A solid = has its own volume and shape and is incompressible.
Liquid = It has its own volume, but does not have its own shape, it is also incompressible.
Aeriform = has neither its own volume nor its own shape. it is compressed.

The properties that help us describe matter are.

Intensive properties: Regardless of the volume (temperature, density) of the material
Comprehensive properties: Depending on the amount of material (mass, volume)
physical properties (such as hardness, density, color, etc.)
Chemical Properties: Characteristic of substances in reactions between different substances.

If these are constant at all points of the substance, then we speak of homogeneous mixtures (such as water and sugar); In contrast, heterogeneous mixtures (such as water and oil: oil does not dissolve in water!)

Homogeneous Mixture

Starting with the homogeneous mix, we do a new subsection, which brings us to keywords like “compound” and “element.”
Suppose we want to divide different parts of a homogeneous mixture, that is, we want to separate from each other.

There are two possibilities:

a) They are detachable
b) They are inseparable

In the first case, the mixture is called a solution.
An example is water and sugar: it is a homogeneous system (or homogeneous mixture) in which the parts, water and sugar, can be separated by physical means (see sedimentation).

Since in the second case two or more components of a mixture cannot be separated by physical means, we speak of a pure substance.
If a pure substance is composed of atoms that are not of similar nature, then we define them as a compound.

Otherwise we are more likely to define it as an element because it is made up of the same types of atoms. For example, an element may be copper while a compound may be bronze, which is formed by the union of copper and tin.

Premise: what is the material

What is matter- The term matter generally refers to anything that has mass and occupies space or, more generally, that is visible and perceptible to our senses.

States of Matter– In order to introduce the overall states of matter, it is important to first remember that atoms, the smallest constituents of matter, can bond to form molecules, and how their union leads to the formation of macroscopic aggregates. It matters.

What is thermodynamic system- The part of matter on which physical observations can be made is called thermodynamic system.

The laws of thermodynamics are fundamental to the study and understanding of physicochemical phenomena and fluctuations in the energy content that result from the passage of a thermodynamic system from one state to another.

Structure of systems- Thermodynamics is able to predict whether, for example, certain reactions may or may not occur spontaneously under certain experimental conditions and regardless of knowledge of the basic structure of matter that makes up the system under investigation.

What is matter in Chemistry

Three types of systems- Based on their ability to exchange energy and matter with the outside world, systems can be divided into three types.

  • isolated when they exchange neither matter nor energy with the outside world.
  • off when they exchange energy from outside (but whatever).
  • Open when they can exchange both energy and matter with the outside world.

Phases of a System- The various parts that make up a system are defined phases and each phase is a part of matter that can be easily separated from others and has constant properties.

Each system can have multiple phases- at this point it is good to point out that a single system can have phases that belong to the three possible states of matter, namely gaseous, liquid, and solid.

Substance in Gaseous State

The main properties of gases- Gas particles can move freely and randomly in all directions, vibrate, because the interaction between them is very weak. The main properties of gases can be traced from the following main points.

The volume of gases is the same as the vessel in which they are contained and depends on pressure and temperature (lack of correct and constant volume).

The particles that make up a gas can move freely in all directions

The particles that make up a gas are generally very far apart from each other and are very small (negligible amounts compared to their population).

Gases are characterized by very low densities

An increase in temperature leads to an increase in the disorder of the gas state. As a result, the kinetic energy of the particles also increases, which occupies and disperses all available space.

Liquid Substance

Properties of liquids- Liquids have a volume of their own, but like gases, they take the shape of the container they are in (so they have no shape of their own).

The intermolecular forces that occur between particles of a liquid are characteristic of gases and solids (strong interactions that can hold particles together under certain conditions).

Free Volume Values of Liquids- Like intermolecular forces, the free volume of liquids also assumes an intermediate value compared to that of solids and gases.

Free volume, a quantity that can be assigned to the three states of aggregation, indicates the volume not occupied by the particles.

In the case of liquids it is estimated to be about 3% of the total volume, in the case of gases it is considerable. More.

Density and surface area of liquids – we also remind you.

  • At the same temperature, the density of a liquid is between that of a gaseous substance and that of a solid (same discourse for compressibility, viscosity, and diffusion)
  • As with solids, the surface of a liquid has different properties than its mass. At the surface, the forces acting on the particles are not balanced. Residual forces result in surface tension that is specific to each liquid (and every solid).

The role of mercury in temperature measurement- The fluctuations in the volume of liquids that occur with temperature can be used for temperature measurement, albeit small.

For example, mercury can be used for this, a liquid that expands homogeneously over wide temperature ranges.

Solid Material

Role of solids- Unlike the two states described in the previous sections, solids have a definite shape. In solids, which also have their own volume.

The interactions are strong and can keep the particles in certain positions (very close to each other). Furthermore, solids have a higher density than gases, are incompressible and do not have the tendency to diffusion.

In the case of solids, the variation in volume as a function of temperature is small.

Vibration Kinetic Energy and Adsorption- The kinetic energy associated with the particles that make up the solid is simply vibration.

Solids are also characterized by a phenomenon known as adsorption, which involves the concentration of a chemical species near the surface.

Two other phenomena related to the nature and intensity of surface interactions are those in which some particles can change from solid to gaseous.

Crystalline solids and amorphous solids- Crystalline solids are characterized by ordered structures, all others are called amorphous.

Crystalline solids have a defined melting temperature, which is the temperature at which the transition from solid to liquid begins at a constant external pressure.

In the case of pure substances, the melting process is completed in a shorter time; On the other hand, amorphous solids do not have an obvious melting point but mainly melt over a wide range of temperatures.

Change in physical state and heat

Change in Physical State: How it Happens- As we have seen, the physical states of matter are determined by the type of forces that exist between the particles that make up the matter under study.

These forces can be changed by withdrawing or providing energy in the form of heat and thus change or change of state.

Bodies that can be in more than one state- Depending on the temperature and pressure conditions in question, there can be many bodies in any of the three states described.

In the case of state changes, which are carried out in closed containers only in the presence of the species investigated, the relevant experimental data are summarized in so-called state diagrams, which are characteristic for each substance.

State diagrams: Equilibrium curves between the physical states of a system- In practice, these are diagrams in which equilibrium curves between the physical states of a given system are plotted.

These curves are created by slowly adding small amounts of heat to the system until equilibrium is reached and slowly recording pressure and temperature readings.


How solidification occurs- Solidification represents the transition from a liquid state to a solid state and occurs at a certain pressure, at a constant temperature.

Introduction to Chemistry – What is Substance

When water cools it turns into ice at 0 °C and the temperature remains constant even though we continue to release heat until everything solidifies.

The latent heat of solidification indicates the amount of heat released by the liquid into the solid during solidification.


How Melting Works- Melting means the opposite path from solid to liquid, from solid to liquid. The melting temperature remains constant until all the solids have gone into the liquid state.

The latent heat of fusion is the heat absorbed by a certain amount of solid during the fusion process.


How Evaporation Happens- Evaporation is the transition from liquid to gas. It affects the surface of the liquid and the rate at which it occurs depends on the temperature, the surface involved and the presence of air currents.

The amount of heat given to bring one mole of liquid or solid to gas state depends only on temperature.

Evaporation and Condensation- A pure liquid in an open container kept at a certain temperature evaporates after a certain amount of time. When the container is closed, a dynamic equilibrium is established.

The number of particles that evaporate in a unit of time is equal to the number of particles moving from vapor to liquid (condensation). Evaporation and condensation rates are the same.

Vapor Pressure or Pressure

How pressure or vapor pressure works The pressure or vapor pressure of a liquid indicates the pressure that is created by the vapor molecules on the liquid in equilibrium and at the temperature in question.

Under similar conditions, the vapor pressure of solids usually does not reach values much higher than that of liquids.

To Boil

Boiling and boiling temperature- by heating a liquid, one can observe the formation of bubbles that rise to the surface and cause strong agitation.

This process is called boiling and occurs at a certain temperature called boiling point . The latter remains constant until all the liquid has evaporated.

Heat of vaporization- The heat of vaporization is rather the (constant) heat required to completely convert a solid amount of a substance from a liquid state to a vapor state.

The boiling point of a substance directly depends on the atmosphere above the liquid: at a pressure of 1 atmosphere (at sea level) water boils at 100 °C, while at higher pressures (for example in the mountains) the boiling temperature decreases. .


What is compaction and how does it work? When vapor is cooled, it transitions to the liquid state: condensation can occur at or below the boiling point at all temperatures (depending on the vapor pressure).

The latent heat of condensation is the amount of heat that must be dissipated for a given amount of substance at a given temperature. The change from gas to liquid state is called liquefaction.

Example of a Heat Curve for a Solid

Thermal Curve of a Solid- The thermal curve of a solid identifies the following phases:

The substance heats up- The heat supplied is used to increase the kinetic energy of the molecules of the solid; Vibrations become more significant and therefore an increase in temperature is observed until the melting point is reached.

The substance melts- During the conversion from solid to liquid, the temperature remains constant, as the heat supplied only serves to increase the potential energy of the particles.

The liquid heats up- The heat supplied is used to raise the kinetic energy of the liquid molecules to the boiling point, at which the molecules can overcome the forces that hold them together in the liquid.

The liquid boils- The temperature remains constant during the transition from liquid to vapor because heat is used to increase the potential energy of the molecules.

The temperature rises because the supplied heat is used to increase the average kinetic energy of the steam molecules.

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