INHOMOGENEOUS SYSTEM: CHARACTERISTICS AND EXAMPLES - CHEMISTRY - 2024

The inhomogeneous system is one that despite its apparent homogeneity, its properties may vary in certain locations in space. The composition of air, for example, even though it is a homogeneous mixture of gases, changes according to altitude.

But what is a system? A system is generally defined as a set of interrelated elements that function as a whole. It can also be added that its elements intervene together to fulfill a specific function. This is the case of the digestive, circulatory, nervous, endocrine, renal and respiratory systems.

Source: Pixabay

However, a system can be something as simple as a glass of water (top image). Note that when adding a drop of ink, it breaks down into its colors and spreads throughout the entire volume of the water. This is also an example of an inhomogeneous system.

When the system consists of a specific space without precise limits such as a physical object, then it is called a material system. Matter has a set of properties such as mass, volume, chemical composition, density, color, etc.

Properties and states of a system

The physical properties of matter are divided into extensive properties and intensive properties.

Extensive properties

They depend on the size of the sample considered, for example its mass and its volume.

The intensive properties

They are those that do not vary with the size of the sample considered. These properties include temperature, density, and concentration.

States of the material

On the other hand, a system also depends on the phase or state in which matter is related to these properties. Thus, matter has three physical states: solid, gas and liquid.

A material can have one or more physical states; such is the case of liquid water in equilibrium with ice, a solid in suspension.

Characteristics of homogeneous, heterogeneous and inhomogeneous systems

Homogeneous system

The homogeneous system is characterized by having the same chemical composition and the same intensive properties throughout. It has a single phase that can be in a solid state, a liquid state or a gaseous state.

Examples of the homogeneous system are: pure water, alcohol, steel, and sugar dissolved in water. This mixture constitutes what is called a true solution, characterized by having the solute a diameter of less than 10 millimicras, being stable to gravity and ultracentrifugation.

-Heterogeneous system

The heterogeneous system presents different values ​​for some of the intensive properties at different sites in the system under consideration. The sites are separated by surfaces of discontinuity, which can be membranous structures or surfaces of the particles.

The coarse dispersion of clay particles in water is an example of a heterogeneous system. The particles do not dissolve in the water and remain in suspension as long as the system is agitated.

When the agitation ceases, the clay particles settle under the action of gravity.

Similarly, blood is an example of a heterogeneous system. It is made up of plasma and a group of cells, among which are erythrocytes, separated from plasma by their plasma membranes that function as discontinuity surfaces.

Plasma and the interior of erythrocytes have differences in the concentration of certain elements such as sodium, potassium, chlorine, bicarbonate, etc.

-Inhomogeneous system

It is characterized by having differences between some of the intensive properties in different parts of the system, but these parts are not separated by well-defined discontinuity surfaces.

Discontinuity surfaces

These discontinuity surfaces can be, for example, the plasma membranes that separate the cell interior from its environment or the tissues that line an organ.

It is said that in an inhomogeneous system the discontinuity surfaces are not visible even using ultramicroscopy. The points of the inhomogeneous system are separated fundamentally by air and aqueous solutions in biological systems.

Between two points of the inhomogeneous system there may be, for example, a difference in the concentration of some element or compound. A temperature difference can also occur between the points.

Diffusion of energy or matter

Under the above circumstances, a passive flow (which does not require energy expenditure) of matter or energy (heat) occurs between the two points of the system. Therefore, the heat will migrate to the colder areas and the matter to the more diluted areas. Thus, the differences in concentration and temperature decrease thanks to this diffusion.

Diffusion occurs by the simple diffusion mechanism. In this case, it fundamentally depends on the existence of a concentration gradient between two points, the distance that separates them and the ease of crossing the medium between the points.

To maintain the concentration difference between the points of the system, a supply of energy or matter is required, since the concentrations at all points would be equal. Therefore, the inhomogeneous system would become a homogeneous system.

Instability

A characteristic to highlight of the inhomogeneous system is its instability, so in many cases it requires a power supply for its maintenance.

Examples of inhomogeneous systems

A drop of ink or food coloring in water

By adding a drop of colorant to the surface of the water, initially the concentration of the colorant will be higher on the surface of the water.

Therefore, there is a difference in the concentration of the dye between the surface of the glass of water and the underlying spots. Furthermore, there is no surface of discontinuity. So, in conclusion this is an inhomogeneous system.

Subsequently, due to the existence of a concentration gradient, the colorant will diffuse into the liquid until the concentration of the colorant is equalized in all the water in the glass, reproducing the homogeneous system.

Water ripples

Source: Pixabay

When a stone is thrown on the surface of the water in a pond, a disturbance occurs that propagates in the form of concentric waves from the impact site of the stone.

The stone when impacting a number of water particles transmits energy to them. Therefore, there is an energetic difference between the particles initially in contact with the stone and the rest of the water molecules on the surface.

As there is no surface of discontinuity in this case, the observed system is inhomogeneous. The energy produced by the impact of the stone spreads on the surface of the water in a wave form, reaching the rest of the water molecules on the surface.

Inspiration

The inspiration phase of respiration, briefly occurs in the following way: when the inspiratory muscles contract, especially the diaphragm, there is an expansion of the rib cage. This results in a tendency to increase the volume of the alveolus.

Alveolar distention causes a decrease in intraalveolar air pressure, making it less than atmospheric air pressure. This produces a flow of air from the atmosphere to the alveoli, through the air ducts.

Then, at the beginning of inspiration, there is a pressure difference between the nostrils and the alveoli, in addition to the non-existence of discontinuity surfaces between the mentioned anatomical structures. Therefore, the present system is inhomogeneous.

Expiration

In the expiration phase, the opposite phenomenon occurs. Intraalveolar pressure becomes higher than atmospheric pressure and air flows through the air ducts, from the alveoli to the atmosphere, until the end-expiratory pressures equalize.

So, at the beginning of expiration there is the existence of a pressure difference between two points, the pulmonary alveoli and the nostrils. In addition, there are no surfaces of discontinuity between the two anatomical structures indicated, so this is an inhomogeneous system.

References

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2. Martín V. Josa G. (February 29, 2012). National University of Cordoba. Recovered from: 2.famaf.unc.edu.ar
3. Chemistry classes. (2008). Physical chemistry. Taken from: clasesdquimica.wordpress.com
4. Jiménez Vargas, J. and Macarulla, JM Fisicoquímica Fisiológica. 1984. Sixth Edition. Editorial Interamericana.
5. Ganong, WF Review of Medical Physiology. 2003 Twenty-First Edition. McGraw-Hill Companies, inc.