It is known that everything that surrounds a person, including himself, are bodies consisting of substances. Those, in turn, are built from molecules, the latter from atoms, and they are from even smaller structures. However, the surrounding diversity is so great that it is difficult to imagine even some kind of commonality. And there is. Compounds number in the millions, each of them is unique in properties, structure and role. In total, several phase states are distinguished, according to which all substances can be correlated.
States of matter
There are four options for the aggregate state of compounds.
- Gases.
- Solids.
- Liquids.
- Plasma is highly rarefied ionized gases.
In this article, we will consider the properties of liquids, their structural features and possible performance parameters.
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 particles that make up the compound.
- Such liquids that consist of atoms held together by Van der Waals forces. Examples are liquid gases (argon, methane and others).
- Substances that consist of two identical atoms. Examples: liquefied gases - hydrogen, nitrogen, oxygen and others.
- Liquid metals - mercury.
- Substances consisting of elements linked by covalent polar bonds. Examples: hydrogen chloride, hydrogen iodide, hydrogen sulfide and others.
- Compounds in which hydrogen bonds are present. Examples: water, alcohols, ammonia in solution.
There are also special structures - like liquid crystals, non-Newtonian liquids, which have special properties.
We will consider the basic properties of a liquid that distinguish it from all other states of aggregation. First of all, these are those that are commonly called physical.
Properties of liquids: shape and volume
In total, about 15 characteristics can be distinguished that allow us to describe what the substances in question are and what their value and features are.
The very first physical properties of a liquid that come to mind at the mention of this state of aggregation is 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 to consider it absent. However, this is not the case.
Under the action of the well-known force of gravity, drops of matter undergo some deformation, so their shape is broken and becomes indefinite. However, if you place a drop in conditions under which gravity does not actor severely limited, then it will take the ideal shape of a ball. Thus, given the task: "Name the properties of liquids," a person who considers himself well-versed in physics should mention this fact.
As for the volume, here we should note the general properties of gases and liquids. Both of them are able to occupy the entire volume of the space in which they are, limited only by the walls of the vessel.
Viscosity
Physical properties of liquids are very diverse. But one of them is unique, such as viscosity. What is it and how is it defined? The main parameters on which the value under consideration depends are:
- tangential stress;
- moving speed gradient.
The dependence of the indicated values is linear. If we explain in simpler words, then viscosity, like volume, is such 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 different from non-Newtonian fluids, which are more viscous and can leave holes behind them that fill up over time.
What will this indicator depend on?
- From temperature. With increasing temperature, the viscosity of some liquids increases, while others, on the contrary,decreases. It depends on the specific compound and its chemical structure.
- From pressure. An increase causes an increase in the viscosity index.
- From the chemical composition of matter. Viscosity changes in the presence of impurities and foreign components in a sample of a pure substance.
Heat capacity
This term refers to 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 have more, others less heat capacity.
So, for example, water is a very good heat accumulator, which allows it to be widely used for heating systems, cooking and other needs. In general, the heat capacity index is strictly individual for each individual liquid.
Surface tension
Often, having received the task: "Name the properties of liquids," they immediately recall surface tension. After all, children are introduced to him at the lessons of physics, chemistry and biology. And each item explains this important parameter from its own side.
The classical definition of surface tension is the following: it is a phase boundary. That is, at the time when the liquid has occupied a certain volume, it borders on the outside with a gaseous medium - air, steam or some other substance. Thus, phase separation occurs at the point of contact.
At the same time, the molecules tend to surround themselves with as many particles as possible and, thus, lead, as it were, tocompressing the fluid as a whole. Therefore, the surface seems to be stretched. The same property can also explain the spherical shape of liquid droplets in the absence of gravity. After all, it is this form that is ideal from the point of view of the energy of the molecule. Examples:
- soap bubbles;
- boiling water;
- liquid drops in weightlessness.
Some insects have adapted to "walk" on the surface of the water precisely due to surface tension. Examples: water striders, waterfowl, some grubs.
Colour
There are common properties of liquids and solids. One of them is fluidity. The whole difference is that for the former it is unlimited. What is the essence of this parameter?
If you apply an external force to a liquid body, it will split into parts and separate them from each other, that is, it will 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
These include three parameters that characterize the substances we are considering:
- overheat;
- cooling;
- boiling.
Such properties of liquids as superheating and hypothermia are directly related to the critical boiling and freezing points (points), respectively. An overheated liquid is called a liquid that has overcome the threshold of the critical heating point when exposed to temperature, but has not shown external signs of boiling.
Supercooled, respectively, calleda liquid that has passed the threshold of the critical point of transition to another phase under the influence of low temperatures, but has not become a solid.
In both the first and second cases, there are conditions for the manifestation of such properties.
- No mechanical effects on the system (movement, vibration).
- Uniform temperature, without sudden jumps and drops.
An interesting fact is that if you throw a foreign object into a superheated liquid (for example, water), it will instantly boil. You can get it by heating under the influence of radiation (in a microwave oven).
Coexistence with other phases of substances
There are two options for this parameter.
- Liquid - gas. Such systems are the most widespread, since they exist everywhere in nature. After all, the evaporation of water is part of the natural cycle. In this case, the resulting steam exists simultaneously with liquid water. If we talk about a closed system, then evaporation occurs there too. It's just that the steam becomes saturated very quickly and the whole system as a whole comes to equilibrium: liquid - saturated steam.
- Liquid - solids. Especially on such systems, one more property is noticeable - wettability. In the interaction of water and a solid, the latter can be wetted completely, partially, or even repel water. There are compounds that dissolve in water quickly and practically indefinitely. There are those that are not capable of this at all (some metals, diamond and others).
In general, the discipline of hydroaeromechanics is engaged in the study of the interaction of liquids with compounds in other states of aggregation.
Compressibility
The basic properties of a fluid would be incomplete if we didn't mention 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 a gas can be compressed quickly and under low pressure, then liquids are compressed unevenly, for a long time and under specially selected conditions.
Evaporation and condensation of liquids
These are two more properties of the liquid. Physics gives them the following explanations:
- Evaporation is the process that characterizes the gradual transition of a substance from a liquid state of aggregation to a solid state. This happens under the influence of thermal effects on the system. Molecules begin to move and, changing their crystal lattice, pass into a gaseous state. The process can continue until all the liquid is converted to vapor (for open systems). Or until equilibrium is established (for closed vessels).
- Condensation is a process opposite to the one indicated above. Here the vapor passes into liquid molecules. This happens until an equilibrium or a complete phase transition is established. The steam releases more particles into the liquid than it does to it.
Typical examples of these two processes in nature are the evaporation of water from the surface of the World Ocean, its condensation inupper atmosphere and then fallout.
Mechanical properties of fluid
These properties are the subject of study of such a science as hydromechanics. Specifically, its section, the theory of fluid and gas mechanics. The main mechanical parameters characterizing the considered state of aggregation of substances include:
- density;
- share;
- viscosity.
Under the density of a liquid body understand 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 entered in special tables.
Specific gravity is considered to be the weight of one unit volume of liquid. This indicator is highly dependent on temperature (as it rises, its weight decreases).
Why study the mechanical properties of liquids? This knowledge is important for understanding the processes occurring in nature, inside the human body. Also when creating technical means, various products. After all, 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 the object of study of physics, as well as some related disciplines. However, in addition to traditional liquid substances, there are also so-called non-Newtonian ones, which are also studied by this science. What are they and why did they getwhat is the title?
To understand what these compounds are, here are the most common household examples:
- "Slime" played by children;
- "hand gum", or chewing gum for hands;
- regular construction paint;
- solution of starch in water, etc.
That is, these are liquids whose viscosity obeys the velocity gradient. The faster the impact, the higher the viscosity index. Therefore, when a hand-gum hits the floor with a sharp blow, it turns into a completely solid substance that can break into pieces.
If you leave it alone, then in just a few minutes it will spread into a sticky puddle. Non-Newtonian liquids are quite unique substances in terms of their properties, which have been used not only for technical purposes, but also for cultural and everyday purposes.
