A material system , in chemistry and other sciences, corresponds to a portion of the universe formed by matter and that is separated from the surroundings in order to study it.
For example, when a chemist says that he is going to study the properties of a solution, said solution corresponds to a material system, since it is made up of matter, and the chemist studies it separately from the surroundings.
Properties of material systems
They have mass and occupy a place in space
This property comes from the simple fact of being made up of matter. This is defined as everything that has mass and volume , so, being made up of matter, systems will also have mass and volume.
These two properties are general for any system, regardless of its composition, and are extensive properties , since they depend on the amount of matter it contains.
They can be of any size
As long as they are composed of matter and there is a well-defined boundary with the surroundings, material systems can be as small or as large as desired.
For example, particle physicists study matter on scales even smaller than the size of an atom. In these cases, the system can be formed by the region where two protons collide at high speed to fragment into tiny particles called quarks.
On the other hand, cosmologists studying distant galaxies, black holes, and all kinds of exotic celestial objects are also studying material systems on unimaginably huge scales.
It has well defined borders
One of the most important characteristics in defining a system is that it can be clearly distinguished where the system ends and the surroundings begin. This means that a material system must have well-defined boundaries.
It is also important to be able to define or know the characteristics of these borders, since this facilitates their study.
For example, a system can be a gas contained in a cylinder with a movable piston that allows its volume to be compressed or expanded, or it could be confined in a rigid metallic reactor that does not allow changes in its shape and volume.
On the other hand, another system could be a cup of coffee confined in a thermos whose walls are adiabatic (which do not allow heat transfer to or from the system).
Material systems also have a series of properties that do not depend on their size or the amount of matter but rather on the kind of matter from which they are made.
Some examples of properties that characterize a material system are color, brightness, thermal and electrical conductivity, density , etc.
Classification of material systems
Material systems can be very varied depending on the characteristics of the matter that composes them. In the first place, two classes of material systems can be distinguished according to the number of different phases that we can distinguish with the naked eye. These are the homogeneous systems, the heterogeneous and the inhomogeneous systems.
These systems in turn can be divided into other classes of material systems according to their composition.
1. Classification of material systems according to the number of phases
When we observe a material system with the naked eye or even with the help of a microscope, we may or may not distinguish parts of the system that are different from each other. This results in different kinds of systems:
Homogeneous material systems
They are those in which only one class of matter is distinguished, even when looking at the system very closely with the use of a microscope. Homogeneous systems are characterized because their properties are exactly the same in any part of the system that is observed.
All regions of a homogeneous system have exactly the same composition and therefore the same intensive properties such as color, density, etc. Homogeneous systems are said to be made up of a single phase of matter.
Pure water is an example of a homogeneous system, since it is impossible to distinguish one drop of water from another in a glass filled with water. Furthermore, any drop of water that we take from one side of the system will have the same characteristics and properties as any other drop taken from another part of the system.
A block of bronze or any other alloy is also an example of a homogeneous material system, since it has a uniform composition throughout.
Heterogeneous material systems
Heterogeneous systems are those that, with the naked eye or with the use of a microscope, can be seen to be made up of more than one phase. This means that regions of the system with different characteristics can be seen and that are physically separated from the others by means of defined borders.
A heterogeneous system is made up of several unmixed phases of homogeneous systems.
Sand and granite are classic examples of heterogeneous systems, since when you look closely you can clearly see that they are made up of particles of different sizes, shapes and colors.
A meat steak is also a heterogeneous system, since areas where there is red tissue and others where there is white fat are clearly distinguished.
Inhomogeneous material systems
These are systems that appear homogeneous at first glance, since different phases are not clearly distinguished, but have different compositions and properties in different parts. They are characterized by presenting a gradual and continuous change of composition and properties from one region of the system to another.
An example is the atmosphere , which is made up of air, an apparently homogeneous gaseous substance. However, if the air in the upper atmosphere is analyzed and compared with that at sea level, it is observed that above it is less dense, contains a lower concentration of oxygen, has a different temperature, etc. Therefore, it is an inhomogeneous system.
2. Classification of material systems according to their composition
Pure substances are homogeneous systems made up of a single class of substance. They can be recognized because it is not possible to separate them into other simpler substances by physical means such as filtration, distillation, evaporation, etc.
Pure substances can be of two types:
- Elements or elemental substances : these cannot be separated into other simpler substances by physical or chemical means.
- Compounds : are those pure substances formed by more than one element.
Gaseous oxygen, metallic iron, and liquid bromine are examples of pure elemental substances.
On the other hand, water, carbon dioxide, and sulfuric acid are examples of compounds.
Mixtures are material systems made up of more than one pure substance. Two types of mixtures can be distinguished:
- Homogeneous mixtures: also called solutions, are those in which all the substances are in a single phase.
- Heterogeneous mixtures: they are mixtures in which the substances are in clearly distinguishable different phases from each other.
Seawater is an example of a homogeneous mixture of water and salt. Alcoholic beverages are also alcoholic, since they are made up of water, alcohol and other substances, all in the same phase.
A piece of wood is a material system made up of a large amount of substances mixed in different phases, making it a heterogeneous mixture.