It is known that everything that surrounds a person, including himself, is bodies made up of substances. Those, in turn, are built from molecules, the last from atoms, and they from even smaller structures. However, the surrounding diversity is so great that it is difficult to imagine even some kind of community. And there is. Compounds are 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
Four variants of the state of aggregation of compounds can be named.
- Gases
- Solids.
- Liquids.
- Plasma is a highly rarefied ionized gas.
In this article we will consider the properties of liquids, the features of their structure and possible parameters of the characteristics.
Fluid classification
The basis of this division is 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, which are composed of atoms held together by the forces of Van der Waals. Examples are liquid gases (argon, methane and others).
- Such substances, which consist of two identical atoms. Examples: gases in a liquefied form - hydrogen, nitrogen, oxygen and others.
- Liquid metals are mercury.
- Substances consisting of elements connected 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 - such as liquid crystals, non-Newtonian fluids, which have special properties.
We will consider the basic properties of a liquid that distinguish it from all other aggregate states. First of all, these are those that are called physical.
Properties of liquids: shape and volume
In total, about 15 characteristics can be distinguished that allow us to describe what constitutes the substances in question and what their value and features are.
The very first physical properties of a fluid 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, it is not.
Under the influence of the well-known gravity, drops of a substance undergo a certain deformation, therefore their shape is violated and becomes undefined. However, if you place a drop in conditions under which gravity does not act or is very limited, then it will take the ideal shape of a ball. Thus, having received the task: “Name the properties of liquids”, a person who considers himself versed in physics should mention this fact.
As for the volume, the general properties of gases and liquids should be noted here. Both of them are able to occupy the entire volume of the space in which they are located, limited only by the walls of the vessel.
Viscosity
The physical properties of the fluid are very diverse. But unique is the viscosity. What is it and what determines it? The main parameters on which the considered value depends are:
- shear stress;
- motion speed gradient.
The dependence of these quantities is linear. If we explain it in simpler words, then viscosity, as well as volume, are such properties of liquids and gases that are common to them and imply unlimited movement regardless of external forces. 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 the difference from non-Newtonian fluids, which have a higher viscosity and can leave holes that fill with time after the movement.
What will this indicator depend on?
- From temperature. With increasing temperature, the viscosity of some liquids increases, while others, on the contrary, decrease. It depends on the particular compound and its chemical structure.
- From pressure. An increase causes an increase in viscosity.
- From the chemical composition of the substance. Viscosity changes in the presence of impurities and extraneous components in a sample of a pure substance.
Heat capacity
This term defines the ability of a substance to absorb a certain amount of heat in order to increase its own temperature by one degree Celsius. There are different compounds for this indicator. Some have a larger, 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 the surface tension. After all, he is introduced to children in physics, chemistry and biology classes. And each subject explains this important parameter for its part.
The classic definition of surface tension is as follows: this is the phase boundary. That is, at a 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.
In this case, the molecules tend to surround themselves with as many particles as possible and, thus, lead, as it were, to compress the liquid as a whole. Therefore, the surface seems to stretch. The same property can also explain the spherical shape of the liquid droplets in the absence of gravity. After all, just such a form is ideal in terms of the energy of the molecule. Examples:
- bubble;
- boiling water;
- drops of liquid in zero gravity.
Some insects have adapted to “walk” on the surface of the water precisely because of surface tension. Examples: water striders, water beetles, some larvae.
Fluidity
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 an external influence is applied to the liquid body, then it will be divided into parts and separate them from each other, that is, 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.
Temperature dependence
These include three parameters that characterize the substances we are considering:
- overheat;
- cooling;
- boiling.
Such properties of liquids as overheating and supercooling are directly related to critical boiling and freezing temperatures (points), respectively. An overheated liquid is a liquid that has crossed the threshold of a critical heating point when exposed to temperature, but has not given any external signs of boiling.
Accordingly, supercooled is a liquid that has crossed the threshold of the critical point of transition to another phase under the influence of low temperatures, but has not become solid.
Both in the first and in the second case, there are conditions for the manifestation of such properties.
- Lack of mechanical effects on the system (movement, vibration).
- Uniform temperature, without sharp jumps and drops.
An interesting fact is that if a foreign object is thrown into an overheated liquid (for example, water), it will boil instantly. 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.
- Liquid is 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 vapor exists simultaneously with liquid water. If we talk about a closed system, then there is evaporation. It’s just that the steam becomes saturated very quickly and the whole system as a whole comes to equilibrium: the liquid is saturated steam.
- Liquid - solids. Especially on such systems, another property is noticeable - wettability. In the interaction of water and a solid, the latter can be wetted completely, partially or completely repel water. There are compounds that dissolve in water quickly and almost unlimitedly. There are those that are not capable of this at all (some metals, diamonds and others).
In general, the discipline of hydroaeromechanics is engaged in the study of the interaction of liquids with compounds in other aggregate states.
Compressibility
The basic properties of a fluid would be incomplete if we had not mentioned compressibility. Of course, this parameter is more characteristic of 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, the liquids are compressed unevenly, for a long time and under specially selected conditions.
Evaporation and condensation of liquids
These are two more properties of a liquid. Physics gives them the following explanations:
- Evaporation is the process that characterizes the gradual transition of a substance from a liquid state to a solid state. This happens under the influence of thermal effects on the system. Molecules move and, changing their crystal lattice, pass into a gaseous state. The process can occur until all the liquid has passed into steam (for open systems). Or until equilibrium is established (for closed vessels).
- Condensation is the opposite of the process indicated above. Here, the vapor passes into the liquid molecules. This happens until equilibrium or a complete phase transition is established. Steam gives more particles to the liquid than it gives it.
Typical examples of these two processes in nature are the evaporation of water from the surface of the oceans, its condensation in the upper atmosphere, and then precipitation.
Fluid mechanical properties
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;
- specific gravity;
- viscosity.
The density of a liquid body is understood to mean its mass, which is contained in one unit of volume. This indicator for different compounds varies. There are already calculated and experimentally measured data on this indicator, which are listed in special tables.
Specific gravity is considered to be the weight of one unit volume of liquid. This indicator is highly dependent on temperature (with increasing 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 - this is 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, and this science is also studying them. What are they and why did they get such a name?
To understand what these compounds are, we will give the most common household examples:
- the "slime" that children play;
- "hand gum", or chewing gum for hands;
- ordinary building paint;
- starch solution in water and so on.
That is, these are liquids whose viscosity obeys the velocity gradient. The faster the exposure, the higher the viscosity. Therefore, with a sharp hit of the hand gum on the floor, it turns into a completely solid substance that can split into parts.
If you leave him alone, then literally a few minutes later it will spread into a sticky puddle. Non-Newtonian fluids are substances that are quite unique in their properties, which have found application not only for technical purposes, but also in cultural and domestic ones.