Liquid

We explain what a liquid is, what its properties are and multiple examples. In addition, we tell you what the fluidity of liquids is.

What is a liquid?

The liquid state is one of the four states of aggregation of matter along with the solid, gaseous and plasmatic states, that is, one of the four ways in which matter occurs in the universe. But unlike the rest, liquids are characterized by being fluid and not having a fixed shape but they assume that of the container that contains them. This is because its particles relate to each other in a loose way, intermediate between the rigidity of solids and the dispersion of gases.

Although most of the matter in the universe exists in the form of gas, almost all known substances can exist as liquids as long as the appropriate pressure and temperature conditions are given. In fact, an increase in temperature can turn a liquid into a gas (evaporation), just as a decrease in temperature can turn it into a solid (freezing). Even so, liquids are more similar to solids than to gases, and this is why they are considered part of “condensed matter.”

Broadly speaking, liquids can be of two types:

• pure liquids composed of the same substance.
• Mixed liquids composed of two or more liquids mixed or by a liquid and one or several solids dissolved in it.

See also: Solid, liquid and gas

Properties of liquids

Liquids have the following physical properties:

• lack a defined shape that is, they acquire that of the container where they are contained.
• are incompressible that is, they cannot be compressed, so their volume is almost constant.
• They present, like solids, a high density but unlike them, have the ability to flow that is, to pass through any hole as long as the destination container is at the same level. This is because the liquid can deform without the need to exert mechanical stress.
• have viscosity that is, resistance to free flow, depending on the nature of the liquid. The higher the viscosity, the slower the flow.
• are adherents that is, they adhere to surfaces, which allows moistening (in other words, getting wet).
• have surface tension which is a force manifested on its surface, capable of resisting to a certain extent the deformation caused by another body. This force is what allows, for example, tree leaves to float on the water of a lake without sinking.
• have capillarity that is, the ability to go against gravity in certain materials when their adhesion strength exceeds their cohesion strength. For example, when the end of a hanging cloth is soaked, the moisture can rise up the cloth to a certain point.

What is fluidity of liquids?

Fluidity is one of the main properties of liquids, which they share with gases. This property allows them to deform and pass through a hole, no matter how small, as well as spill onto a different surface. Substances endowed with this property are known as fluids.

Examples of liquids

Some examples of liquid substances, both pure and mixed, are:

• Water, the most abundant liquid on the planet.
• Volcanic lava, as long as it stays hot.
• Human or animal blood.
• The milk of mammals.
• Mercury, the only liquid metal at room temperature.
• Kerosene, fuel derived from petroleum.
• Hydrogen peroxide from first aid kits.
• Sunflower oil used for cooking.
• The sulfuric acid present in acid rain.
• The olive oil used for cooking.
• Acetone used as a solvent.
• The sweat secreted by the skin glands.
• The sap of plants and trees.
• Natural gas subjected to high pressures (liquefied) inside a cylinder.
• The ink inside the pens.
• Vinegar or ascetic acid.
• The urine secreted by the kidneys of animals.
• Rubber paints for interiors or exteriors.
• The hemolymph of insects and other arthropods.
• The venom secreted by snakes.
• Nitroglycerin, a highly explosive liquid compound.
• Chloroform, a colorless liquid with a pungent odor used in the chemical industry.
• Lemon juice or other squeezed citrus fruits.
• Tea infusions or other herbs.
• Pitch, a black organic liquid of such viscosity that it appears solid.
• Saliva generated in the human mouth.
• Ethyl alcohol, product of the fermentation of natural substances.
• Gasoline refined from certain petroleum derivatives.
• Methanol, also called wood alcohol or burning alcohol.
• Chlorine solutions used as a cleaner and solvent.

The other states of matter

In addition to the liquid state, matter can exist in three other physical states:

• The solid state in which the particles are closely organized, so much so that they exert significant resistance to changes in shape and volume. It is a very cohesive condensation state, which can however be made liquid by introducing heat energy.
• The gaseous state in which the particles are much more dispersed and separated than in the liquid state, so the substance does not have its own shape and volume, but rather adopts those of the container or environment that contains it. Gases have a weak interaction between their particles, but through increased pressure they can be forced to acquire liquid form (liquefaction).
• The plasma state in which the particles are in a gas-like dispersion state, but at the same time are electromagnetically charged (ionized). Plasma is the state of aggregation of the most abundant matter in the universe, whose great and main example is the Sun.

Continue with: Properties of matter

References

• “Characteristics of liquids” at the Autonomous University of the State of Hidalgo (Mexico).
• “Liquid state” in the Ministry of Education of Spain.
• “Liquid (state of matter)” in The Encyclopaedia Britannica.