MATERIAL SYSTEMS: CLASSIFICATION, PHASES AND EXAMPLES - CHEMISTRY - 2025

The material systems are those that are composed of matter and which are isolated from the rest of the universe to be studied. Matter is everywhere, giving form and real meaning to the perceptions of daily life, but when it is desired to study a portion of matter, its surroundings are despised and we speak of a material system.

They are highly variable, since there are pure and composite materials, as well as different states and phases of aggregations. How to define the boundary between the material system and its surroundings? It all depends on the variables that are considered. For example, in the image below each candy marble could be the system under study.

However, if the color variable is to be taken into account, then it is necessary to consider all the marbles in the vending machine. Because the machine is not of interest, this is the environment of the marbles. Thus, the material system of the example comes to be the mass of the marbles and their properties (be these of gum, mint, etc.).

However, chemically, material systems are defined as any pure substance or a mixture thereof, classified according to their physical aspects.

Classification

Homogeneous material system

The matter being studied can show a uniform appearance, in which its properties remain constant regardless of the sample being analyzed. In other words: this kind of system is characterized by having only one phase of matter at first glance.

Pure substance and compounds

If a pure substance is analyzed, then the physicochemical properties will be found to coincide in the same values ​​and results, even if many samples are taken (and in different geographical areas).

For example, if a calcium sample were compared to one from Asia, Europe, Africa, and America, they would all have the same properties. The same would happen if a sample of pure carbon was taken.

On the other hand, a pure compound also manifests the above mentioned. If it were guaranteed that a slate was made of one and only material, then it would be classified as a homogeneous material system.

However, this does not happen for a mineral sample, since in general it harbors impurities from other associated minerals, and for this case it is a heterogeneous material system. Likewise, those material systems such as trees, stones, mountains, or rivers fall into the latter classification.

Dissolution

Commercial vinegar is a 5% aqueous solution of acetic acid; that is, 5 mL of pure acetic acid is dissolved in 100 mL of water. However, it looks like a transparent liquid, even though it is actually two pure compounds (water and acetic acid) combined.

Heterogeneous material system

In contrast to the homogeneous one, in this class of system neither the appearance nor the properties are constant, being irregular throughout its extension.

In addition, it can be subjected to physical or chemical separation techniques, from which phases are extracted that are each considered as a homogeneous system.

Phases

The upper image shows the states of matter and their changes. These are closely related to the phases of matter because, while they are the same, they do have some subtle differences.

Thus, the phases of a material system are the solid, the liquid and the gas. That is to say, for certain matter subjected to analysis, it can adopt any of the previous phases.

However, since the interactions in solids are very strong and they depend on variables such as pressure and temperature, a system may or may not have different solid phases.

For example, compound X, solid at room temperature, has phase I; but when the pressure on it is very high, its molecules rearrange in a more compact way, and then a transition occurs from phase I to solid phase II.

There are even other phases, such as III and IV, that derive from II at different temperatures. Thus, the homogeneous material system of X of an apparent solid phase can acquire up to four solid phases: I, II, III and IV.

In the case of liquid and gaseous systems, generally the molecules can only adopt a single phase in these states of matter. In other words, there may not be a gas phase I and a gas phase II.

Phase diagram

There are many phase diagrams: some for a single compound or substance (like the one in the image above), and others for binary systems (a salt in water, for example) or ternary (three components).

The "simplest" of all is the phase diagram for a substance. Thus, for the hypothetical substance Y, its phase is represented as a function of pressure (y-axis) and temperature (x-axis).

At low pressures it is a gas, regardless of its temperature. However, when increasing the pressure Y gas is deposited in solid Y.

However, at temperatures above the critical point Y, the gas condenses into liquid Y, and if the pressure is also increased (one rises vertically through the diagram), the liquid solidifies.

Each line represents the equilibrium between the two phases that it separates: solid-gas, liquid-gas, solid-liquid, liquid-solid and solid-liquid-gas at the triple point.

Additionally, from the critical point Y no physical distinction is shown between the gas phase and the liquid phase: it forms what is known as a supercritical fluid.

Examples

- A balloon is a material system, since its content is gaseous and, therefore, has a chemical nature; if the gas is less dense than air, the balloon will rise to the sky.

- The water-oil binary system has two phases: one of water and the other, logically, of oil. The set of both is the heterogeneous system, while the individual layers are homogeneous systems. If you wanted to extract the oil, you would need to perform a liquid-liquid extraction with an organic and volatile solvent.

- A solid-solid system can consist of a mixture of white sugar and brown sugar. Here, the difference in color between the crystals makes this case a heterogeneous system.

- Sea water is another example of a homogeneous material system. It consists of a dissolution of many ions, which are responsible for its characteristic salty taste. If a sample of seawater were to evaporate in a container, it would settle in white salts.

References

1. A System and Its Surroundings. Retrieved on May 27, 2018, from: chem.libretexts.org
2. Antonio de Ulloa. Material systems.. Retrieved on May 27, 2018, from: 2.educarchile.cl
3. Daniel J. Berger. (2001). Retrieved on May 27, 2018, from: bluffton.edu
4. The System and the Surroundings in Chemistry. Retrieved on May 27, 2018, from: chemteam.info
5. Helmenstine, Anne Marie, Ph.D. (February 6, 2018). Open System Definition in Chemistry. Retrieved on May 27, 2018, from: thoughtco.com
6. Glen Research Center. Phases of Matter. Retrieved on May 27, 2018, from: grc.nasa.gov
7. Alison H. (2006-09-15). Balloon Launch. Retrieved on May 28, 2018, from: flickr.com