LIQUID STATE: CHARACTERISTICS, EXAMPLES - CHEMISTRY - 2025

The liquid state is one of the main physical states that matter adopts and that is abundantly observed in the hydrosphere of the Earth, but not with regard to the Cosmos and its incandescent or icy temperatures. It is characterized by flowing and being more compact than gases. For example, seas, rivers, lakes and oceans flow and are in a liquid state.

The liquid is the "bridge" between the solid and gaseous states for a given substance or compound; A bridge that can be small or extremely wide, which shows how stable the liquid is in relation to the gas or solid, and the degree of its cohesion forces between its constituent atoms or molecules.

Waterfalls and rivers are a clear example of the ability of water to flow. Source: florianpics04 from Pixabay.

Then by liquid is understood all that material, natural or artificial, capable of flowing freely in favor or against gravity. In waterfalls and rivers the flow of fresh water currents can be seen, as well as in the sea the displacement of its foamy ridges and their breaking on the coasts.

Water is the earthly liquid par excellence, and chemically speaking it is the most exceptional of all. However, established the required physical conditions, any element or defined compound can go to the liquid state; for example, salts and liquid gases, or a refractory mold filled with molten gold.

Characteristics of the liquid state

They have no definite shape

Unlike solids, liquids need a surface or container to acquire variable shapes.

Thus, due to irregularities in the terrain, rivers “meander”, or if a liquid is spilled on the ground, it spreads as its surface wets. Likewise, by filling containers or containers of any geometry or design to satiety, liquids take their shapes occupying their entire volume.

They have a dynamic surface

Solids also adopt surfaces, but they are virtually (since they can erode or corrode) independent of their environment or the container that stores them. Instead, the surface of the liquids always adjusts to the width of the container, and its area can oscillate if it is shaken or touched.

The surfaces of liquids are dynamic, they move constantly even if they cannot be seen with the naked eye. If a stone is thrown into an apparently calm pond, the appearance of concentric waves will be observed that travel from the point where the stone fell, towards the edges of the pond.

They are incomprehensible

Although there are exceptions, most liquids are incomprehensible. This means that enormous pressure is required to reduce their volumes appreciably.

They are molecularly dynamic

Atoms or molecules have freedom of movement in liquids, so their intermolecular interactions are not strong enough to keep them fixed in space. This dynamic character allows them to interact, solubilizing or not the gases that collide with their surfaces.

They present surface tension

The particles of the liquid interact to a greater degree with each other than with the particles of the gas that hover on its surface. Consequently, the particles that define the surface of the liquid experience a force that attracts them to the bottom, which opposes an increase in their area.

That is why liquids when spilled on a surface that they cannot wet, are arranged as drops, whose shapes seek to minimize their area and thus surface tension.

They are macroscopically homogeneous but can be molecularly heterogeneous

The liquids appear homogeneous to the naked eye, unless they are some emulsions, suspensions, or a mixture of immiscible liquids. For example, if gallium melts we will have a silver liquid wherever we look at it. However, molecularly appearances can be deceptive.

The particles of the liquid move freely, unable to establish a long-range structural pattern. Such an arbitrary and dynamic arrangement can be considered homogeneous, but depending on the molecule, the liquid could host regions of high or low density, which would be heterogeneously distributed; even when these regions move.

Freeze or vaporize

Liquids can usually undergo two phase changes: solid (freezing), or gaseous (vaporization). The temperatures at which these physical changes take place are called melting or boiling points, respectively.

As the particles freeze, they lose energy and become fixed in space, now oriented by their intermolecular interactions. If such a resulting structure is periodic and orderly, it is said that rather than freezing, it has crystallized (as happens with ice).

Freezing is accelerated depending on the speed with which the crystallization nuclei form; that is, small crystals that will grow to be robust.

Meanwhile, in the vaporization all order is broken: the particles acquire energy through heat and escape to the gas phase, where they travel with greater freedom. This phase change is accelerated if the growth of bubbles inside the liquid is favored, which overcome the external pressure and that exerted by the liquid itself.

Examples of liquids

Water

On planet Earth we find in great abundance the strangest and most surprising liquid of all: water. So much so that it makes up what is known as the hydrosphere. The oceans, seas, lakes, rivers and waterfalls represent examples of liquids at their finest.

Lava

Another well-known liquid is lava, burning red hot, which has the characteristic of flowing and running downhill through volcanoes.

Petroleum

Likewise, we can mention oil, a complex, black, oily liquid mixture composed mostly of hydrocarbons; and the nectar of the flowers, like the honeys of the beehives.

In the kitchen

Oils

Liquids are present when cooking. Among them we have: vinegar, wines, Worcestershire sauce, oil, egg white, milk, beer, coffee, among others. And if cooking in the dark, melted candle wax also counts as an example of liquid.

In labs

All solvents used in laboratories are examples of liquids: alcohols, ammonia, paraffins, toluene, gasoline, titanium tetrachloride, chloroform, carbon disulfide, among others.

Gases such as hydrogen, helium, nitrogen, argon, oxygen, chlorine, neon, etc., can be condensed in their respective liquids, which are characterized by being used for cryogenic purposes.

Likewise, there is mercury and bromine, the only liquid elements under normal conditions, and metals with low melting points such as gallium, cesium and rubidium.

References

1. Whitten, Davis, Peck & Stanley. (2008). Chemistry (8th ed.). CENGAGE Learning.
2. Serway & Jewett. (2009). Physics: for science and engineering with Modern Physics. Volume 2. (Seventh edition). Cengage Learning.
3. Wikipedia. (2019). Liquid. Recovered from: en.wikipedia.org
4. Helmenstine, Anne Marie, Ph.D. (July 20, 2019). Liquid Definition in Chemistry. Recovered from: thoughtco.com
5. Belford Robert. (June 05, 2019). Properties of Liquids. Chemistry LibreTexts. Recovered from: chem.libretexts.org