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Properties of liquids. Basic physical properties of a liquid

It is known that everything that surrounds a person, including himself, is a body consisting of substances. Those, in turn, are built of molecules, the last of the atoms, and they are made up of even smaller structures. However, the surrounding diversity is so great that it is difficult to imagine even some kind of community. And there is. Connections are counted in the millions, each of them is unique in its properties, structure and role. In total, several phase states are distinguished, by which all substances can be correlated.

Aggregate states of substances

We can name four variants of the aggregate state of compounds.

  1. Gases.
  2. Solids.
  3. Liquids.
  4. Plasma - strongly rarefied ionized gases.

In this article we will consider the properties of liquids, the features of their structure and possible parameters of the characteristics.

Classification of liquid bodies

This division is based on the properties of liquids, their structure and chemical structure, as well as the types of interactions between the constituent compounds of the compound.

  1. Such liquids, which consist of atoms, are held together by the forces of van der Waals. Examples are liquid gases (argon, methane and others).
  2. Such substances, which consist of two identical atoms. Examples: gases in liquefied form - hydrogen, nitrogen, oxygen and others.
  3. Liquid metals are mercury.
  4. Substances consisting of elements bound by covalent polar bonds. Examples: hydrochloric acid, iodine hydrogen, hydrogen sulphide and others.
  5. Compounds in which hydrogen bonds are present. Examples: water, alcohols, ammonia in solution.

There are also special structures - such as liquid crystals, non-Newtonian fluids, which have special properties.

We shall now consider the basic properties of a liquid that distinguish it from all other aggregate states. First of all, these are those that are usually called physical.

Properties of liquids: shape and volume

In total, about 15 characteristics can be distinguished, which allow us to describe what the substances under consideration are and what their value, features, is.

The very first physical properties of a liquid that come to mind when mentioning this aggregate state are the ability to change shape and occupy a certain volume. So, for example, if we talk about the form of liquid substances, then it is generally accepted that it is absent. However, it is not.

Under the action of all known gravity, droplets of matter undergo some sort of deformation, so their form is disturbed and becomes uncertain. However, if you put a drop in conditions under which gravity does not act or is strongly limited, it will take the ideal shape of the ball. Thus, having received the task: "Name the properties of liquids," a person who considers himself sufficiently versed in physics should mention this fact.

As for the volume, here it is necessary to note the general properties of gases and liquids. Both of them are capable of occupying the entire volume of space in which they are found, confining themselves only to the walls of the vessel.

Viscosity

The physical properties of the liquid are very diverse. But a unique one is such as viscosity. What is it and what is determined? The main parameters on which the value in question depends are:

  • Shearing stress;
  • Velocity gradient.

The dependence of these quantities is linear. If we explain more simple words, the viscosity, like the volume, is the properties of liquids and gases that are common to them and imply unlimited movement regardless of external forces of influence. That is, if water flows out of the vessel, it will continue to do so under any influences (gravity, friction and other parameters).

This is in contrast to non-Newtonian fluids, which have a higher viscosity and can leave behind the motion holes that fill with time.

What will this indicator depend on?

  1. From the temperature. With increasing temperature, the viscosity of some liquids increases, while others, on the contrary, decrease. It depends on the specific compound and its chemical structure.
  2. From the pressure. The increase causes an increase in the viscosity index.
  3. From the chemical composition of matter. The viscosity varies with impurities and foreign components in the sample of the pure substance.

Heat capacity

This term determines the ability of a substance to absorb a certain amount of heat to increase its own temperature by one degree Celsius. There are different connections for this indicator. Some possess greater, some lesser heat capacity.

For example, water is a very good heat accumulator, which allows it to be widely used for heating, cooking and other needs. In general, the heat capacity is strictly individual for each individual fluid.

Surface tension

Often, having received the task: "Name the properties of liquids" immediately recall the surface tension. After all, he is introduced to children at physics, chemistry and biology classes. And each subject explains this important parameter from its side.

The classical definition of surface tension is as follows: this is the phase boundary. That is, at the time when the liquid has occupied a certain volume, it borders on the outside with the gas medium - air, steam or some other substance. Thus, phase separation occurs at the point of contact.

In this case, the molecules tend to surround themselves with as many particles as possible and, thus, lead, as it were, to compressing the liquid as a whole. Consequently, the surface is stretched. The same property can also explain the spherical shape of liquid droplets in the absence of gravity. After all, this form is ideal from the point of view of the energy of the molecule. Examples:

  • bubble;
  • boiling water;
  • A drop of liquid in weightlessness.

Some insects have adapted to "walking" on the surface of the water precisely because of surface tension. Examples: water cannons, waterfowl beetles, some larvae.

Flowability

There are common properties of liquids and solids. One of them is fluidity. The difference is that for the former it is unlimited. What is the essence of this parameter?

If an external action is applied to the liquid body, it will separate into parts and separate them from each other, that is, flow. In this case, each part will again fill the entire volume of the vessel. For solids this property is limited and depends on external conditions.

Dependence of properties on temperature

To these three parameters that characterize the substances we are considering:

  • overheat;
  • cooling;
  • boiling.

The properties of liquids, such as overheating and subcooling, are directly related to the critical boiling point and freezing point, respectively. Overheated is a liquid that has overcome the threshold of the critical point of heating when exposed to temperature, but has not applied external signs of boiling.

The supercooled, respectively, is a liquid that has overcome the threshold of the critical point of transition to another phase under the influence of low temperatures, but has not become solid.

As in the first, and in the second case there are conditions for the manifestation of such properties.

  1. Absence of mechanical effects on the system (motion, vibration).
  2. Uniform temperature, without sudden jumps and drops.

The fact is interesting, that if a foreign object is thrown into a superheated liquid (for example, water), it will instantly boil. It can be obtained by heating under the influence of radiation (in a microwave oven).

Coexistence with other phases of substances

There are two options for this parameter.

  1. The liquid is gas. Such systems are the most widespread, since they exist in nature everywhere. Because the evaporation of water is part of the natural cycle. In this case, the resulting vapor exists simultaneously with liquid water. If we talk about a closed system, then there is evaporation. Simply the steam becomes saturated very quickly and the whole system as a whole comes to equilibrium: liquid - saturated steam.
  2. Liquid is a solid. Especially on such systems, one more property is noticeable: wettability. When water and solid interact, the latter can be wetted completely, partially or even repel water. There are compounds that dissolve in water quickly and practically unlimitedly. There are also those that are generally incapable of doing this (some metals, diamonds and others).

In general, the study of the interaction of liquids with compounds in other aggregate states is concerned with the discipline of hydroaeromechanics.

Compressibility

The basic properties of the liquid would be incomplete if we did not mention the compressibility. Of course, this parameter is more typical for gas systems. However, the ones we are considering can also be compressed under certain conditions.

The main difference is the speed of the process and its uniformity. If the gas can be compressed quickly and under low pressure, then the liquids are compressed unevenly, long enough and under specially selected conditions.

Evaporation and Condensation of Liquids

These are two more properties of the liquid. Physics gives them the following explanations:

  1. Evaporation is the process that characterizes the gradual transition of matter from the liquid aggregate state to the solid state. This occurs under the influence of thermal effects on the system. The molecules move and, changing their crystal lattice, go into a gaseous state. The process can take place until all the liquid goes into steam (for open systems). Or to establish an equilibrium (for closed vessels).
  2. Condensation is a process opposite to the one indicated above. Here the vapor passes into the molecules of the liquid. This occurs before equilibrium is established or a complete phase transition occurs. Steam gives into the liquid more particles than it does to it.

Typical examples of these two processes in nature - the evaporation of water from the surface of the World Ocean, its condensation in the upper layers of the atmosphere, and then precipitation in the form of precipitation.

Mechanical properties of a liquid

These properties are subject to study of such a science as hydromechanics. Specifically, its section, the theory of fluid mechanics and gas. The main mechanical parameters characterizing the aggregate state of matter in question are:

  • density;
  • specific gravity;
  • viscosity.

By the density of a liquid body is understood its mass, which is contained in one unit of volume. This indicator varies for different compounds. There are already calculated and experimentally measured data on this indicator, which are listed in special tables.

The weight is considered to be the weight of one unit of fluid volume. This indicator strongly depends on the temperature (with increasing its weight decreases).

Why should I study the mechanical properties of liquids? This knowledge is important for understanding the processes occurring in nature, within the human body. Also when creating technical means, different products. Liquid substances are one of the most common aggregate forms on our planet.

Non-Newtonian fluids and their properties

The properties of gases, liquids, solids are an object of study of physics, as well as of some related disciplines. However, in addition to the traditional liquid substances, there are also so-called non-Newtonian ones, they are also studying this science. What are they, and why did they get that name?

To understand what such compounds are, let us cite the most common everyday examples:

  • "Lizun" played by children;
  • "Hand ham", or chewing gum;
  • Ordinary building paint;
  • Starch solution in water and so on.

That is, they are liquids whose viscosity is subject to the velocity gradient. The faster the exposure, the higher the viscosity index. Therefore, with a sharp blow to the din of the floor, it turns into a completely solid substance that can split into parts.

If you leave it alone, then in a few minutes it will spread out like a sticky puddle. Non-Newtonian fluids are quite unique in their properties, which have found application not only for technical purposes, but also in cultural and domestic ones.

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