Characteristics of Liquids

A liquid is all substance made up of molecules that are constantly in motioncolliding with each other millions of times per second. It is one of the physical states of matter: the intermediate. The molecules of liquids do not move as freely as those that make up a gas, nor are they as close together as in a solid.

Liquids have a defined volume, but their shape depends on the contour of the container that contains them. Liquids are practically incompressible. Some characteristics of liquids are Viscosity, Surface Tension, Cohesion, Adhesion, Capillarity, Boiling Point, Melting Point.

Viscosity

Viscosity is the resistance of all liquid to flow. Draining liquids encounter this opposition, as a consequence of the combined effects of cohesion and adherence. Viscosity is produced by the sliding effect resulting from the movement of one fluid layer with respect to another, it can be considered as caused by the internal friction of the molecules.

To the increase the temperature of a liquid, viscosity decreases

 invariably and increases with increasing pressure. The higher the viscosity the liquid flows more slowly, on the contrary, the lower the viscosity the liquid flows faster.

Viscosity can be measured by taking the time it takes for a liquid to flow through a thin tube, under the effect of gravity.

In the Transformation industry it is very useful to know the viscosity of a liquid, since you can know what type of liquid is the most suitable to be used in certain machinery so that it works in optimal conditions. The unit of viscosity in the International System is the poiseuille (N * s / m²). In the CGS system, it is the poise (dyne * s / cm²).

Surface tension

In a liquid, each molecule always moves under the influence of its neighboring molecules, the interior molecules attract each other to almost the same magnitude in all directions. However, on the surface of the liquid one molecule is not completely surrounded by others and, as a result, only experiences the attraction of molecules that are below and to the sides.

As a result, the molecules along the surface experience a attraction in a direction into the liquid, which causes the surface molecules to be dragged inside, thus originating the tension surface and causing the surface of the liquid to behave as a thin elastic film and invisible.

Surface tension is responsible for the resistance that a liquid presents to the penetration of its surfaces, of the tendency to the spherical shape of the drops of a liquid, of the rise of the liquids in capillary tubes and of the floating of objects or organisms on the surface of the liquids.

Surface Tension of water is greater than that of many other liquids. It can be measured using a platinum ring that is placed on the surface of the liquid. The force required to separate the ring from the liquid surface is measured with a high precision balance.

It is represented by the Greek letter γ and its units are: N / m in the International System and dyne / cm in the CGS System. The surface tension of liquids can be reduced by dissolving surfactants in them, such as soap powder, which causes soapy particles to penetrate more easily into clothing fabrics.

Cohesion

Cohesion is the attractive force between molecules of a liquid. For example, Alcohol has a lower cohesion force between its molecules than water. For this reason, alcohol volatilizes more quickly. If we deposit drops of alcohol and oil on a glass, it is observed that the alcohol is crushed more than the oil drop, since the cohesion force and the surface tension of the oil are higher than in the alcohol. Due to the cohesive force, two drops of a liquid come together to form one, as is the case with water and mercury.

Adherence

It is defined as Adherence to Attraction Force between molecules of different substances. Most liquid substances adhere to the walls of solid bodies.

If in a liquid the adhesive forces are greater than cohesion forces, the surface of the liquid is attracted to the surface of a solid body. If the cohesion forces are greater than those of adhesion of the liquid, it will not adhere to the surface of the solid, such is the case of mercury, since when a glass rod is inserted into a container full of mercury when it is removed, it is observed that dry.

Capillarity

It is the formation of a concave (sunken) meniscus or formation of a convex (raised) meniscus of the surface of a liquid in the area of ​​contact with a solid, for example, on the walls of a tube.

Capillarity depends on the forces created by surface tension and by the wetting of the walls of a tube. They are examples of capillarity: when the water is absorbed by a sponge, the rise of the wax melted by the wick of a candle, the water when rising through the earth. Fountain pens and down are also designed based on the phenomenon of capillarity.

Boiling point

Boiling Point is the Temperature at which a liquid begins to completely transform into a vapor. If the temperature is raised to a higher, the transition will be faster and the steam will emerge much faster. For example, the Boiling Point of water is at 100 ° C, and that of Ethyl Alcohol is at 78 ° C.

Freezing point

Freezing Point is the Temperature at which a liquid begins to transform into a solid. This is due to the fact that at a lower temperature the particles of the substance begin to lose kinetic energy. They fit in a more compact form. They are ordered, so they reach this state of aggregation. For example, the Freezing Point of Water is at 0 ° C.

Examples of Characteristics of Liquids

Made up of molecules that are constantly in motion

Their shape depends on the contour of the container that contains them

They are practically incompressible

Viscosity

Surface tension

Cohesion

Adherence

Capillarity

Boiling point

Freezing point