The inhomogeneous system It is one that despite its apparent homogeneity, its properties can vary in certain locations in space. The composition of air, for example, even if 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..
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 volume of the water. This is also an example of an inhomogeneous system.
When the system consists of a determined space without precise limits such as a physical object, it is then spoken of as a material system. Matter has a set of properties such as mass, volume, chemical composition, density, color, etc..
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The physical properties of matter are divided into extensive properties and intensive properties.
They depend on the size of the sample considered, for example its mass and its volume.
They are those that do not vary with the size of the sample considered. These properties include temperature, density, and concentration..
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, gaseous 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.
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 solid state, liquid state or 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 less than 10 millimicras, being stable to gravity and ultracentrifugation..
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..
Likewise, 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..
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.
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.
Under the above circumstances, a passive flow (which does not require expenditure of energy) of matter or energy (heat) occurs between the two points of the system. Therefore, heat will migrate to colder areas and matter to more dilute 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 difference in concentration between the points of the system, a supply of energy or matter is required, since the concentrations would be equalized at all points. Therefore, the inhomogeneous system would become a homogeneous system.
A characteristic to highlight of the inhomogeneous system is its instability, which is why in many cases it requires a power supply for its maintenance..
By adding a drop of colorant on 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. Also, there is no discontinuity surface. 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 in all the water in the glass is equalized, reproducing the homogeneous system.
When a stone is thrown on the surface of the water of a pond, a disturbance is produced 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 discontinuity surface 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..
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 produces 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.
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 pressures are equalized at the end of expiration.
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 indicated anatomical structures, so this is an inhomogeneous system..
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