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In many contexts, the terms “phases of matter” and “states of matter” are used interchangeably as if they were synonymous. The same can be said with respect to phase changes and state changes. However, there are subtle differences that make these terms not exactly the same.
Next, we will explore these differences to learn to clearly distinguish when we are talking about phases and when about states of matter.
What are the states of matter?
The states of matter are the different ways in which the particles that make it up can be added or joined together. For this reason, they are also called aggregation states of matter . These states are essentially defined based on the mobility that their particles present in the structure of the substance.
In this sense, the same substance can generally find the following four states of matter:
- Solid state: characterized by being formed by bodies with a defined shape and volume. In the solid state, all particles are confined to a fixed position, with very little freedom of movement. This gives solids both a definite volume and a definite shape.
- Liquid State: in liquids, the particles that make up a substance are very close to each other, but their union is loose enough to allow the particles to flow and slide from one place to another with relative freedom. For this reason, liquids have a defined volume, but not a defined shape, acquiring the shape of the container that contains them.
- Gaseous state: In this state the particles are essentially separate from each other, interacting very little with each other. Substances in the gaseous state are characterized by having very low densities, and by not having a defined shape or volume.
- Plasma: A plasma is a gaseous mixture of free electrons and positive ions (cations) that are formed by heating gases to very high temperatures. These temperatures are so high that when they collide with each other, the atoms literally tear the electrons out of each other. The matter of the stars is in the plasma state, in most of them.
Many substances can exist in any of these states, while others cannot. Water is the typical example of a substance that we can find in a solid, liquid and gas state, even all at the same time under relatively normal conditions. On the other hand, sucrose or common table sugar can exist in a solid state (as we normally find it), and we can also melt it, thus becoming a liquid as when we make caramel. However, if we keep heating the molten sucrose, instead of turning into a gas state, it usually decomposes or carbonizes before turning into a gas state.
In addition to these common states, there are other less common states that only exist under very extreme conditions of temperature and pressure. For example, there is the Bose-Einstein condensate that only forms at extremely low temperatures, very close to absolute zero; the degenerate state of matter that exists under conditions of extremely high densities such as in neutron stars that form after a star dies, and quark-gluon plasmas , which form only under extremely high energy conditions.
Factors Affecting States of Matter
Whether a given substance is in the form of a solid, a liquid or a gas depends on a competition between forces that try to keep its particles together, and the forces that tend to separate them. The forces of interaction that exist between its particles, or cohesive forces, tend to unite the particles, while thermal vibrations tend to separate them. On the other hand, high pressure tends to bring the particles closer together, facilitating the interaction between particles and tending to condense them.
What are the phases of matter?
The concept of phase is different from that of state. In physics and chemistry, a phase of matter refers to a portion of matter or to a zone or region within a system in which the physical and chemical properties are uniform or homogeneous.
This might seem like a concept similar to that of state, since there are cases in which a substance in a physical state is also in the form of a single phase. This happens, for example, in the case of water. Water in a gaseous state, that is, water vapor, is at the same time a phase, since water vapor is essentially homogeneous. The same can be said of liquid water and ice. In these cases, talking about the gaseous phase of water is basically the same as talking about water in a gaseous state.
However, there are other substances that can exist in different forms despite being in the same state. An example is silicon oxide or silica, which can exist in different phases, all of them in the solid state. Depending on temperature and pressure conditions, silica can exist as quartz-a, quartz-β, cristobalite, tridymite, coesite, and more. Each of these phases are all in a solid state and each of them has a particular structure and physical-chemical properties that are different from the others.
Phases in multicomponent systems
The phases and states of matter are easy to understand in the cases of pure substances or systems made up of a single component. However, when we mix various components to form binary, ternary, and more complex systems, unexpected behaviors of matter can arise.
In these cases, a large number of different phases can be formed depending on the composition of the system and the proportions in which the different components are found. Alloys are clear examples of these complex systems in which we can obtain radically different properties by mixing metals together.
The phase concept is also very useful for describing mixtures of immiscible liquids such as oil and water. Although, as a whole, the system is in a liquid state, it is evident that there are two distinct phases, one formed by the oil floating on top of the aqueous phase. Note that, in this case, it does not make sense to speak of an oily or organic “state” and an aqueous “state”, but it does make sense to speak of an oily or organic phase and an aqueous phase.
Summary of the differences between state and phase of matter
The states of matter are defined based on the mobility of the particles that make it up. Instead, the phases of matter are defined in terms of the physical and chemical properties of the matter, and several different phases can be found with the same composition and in the same state of aggregation but which, however, have different properties.
On the other hand, the states of matter can be solid, liquid, gas and plasma, as well as other more exotic states that exist in extreme conditions. On the other hand, several liquid and gas phases and multiple solid phases can coexist in the same system. This indicates that the concept of state of matter is a more general or less specific concept than the phase of matter.
References
Difference Between Phase and State . (2015, October 11). dokumen.tips. https://dokumen.tips/documents/difference-between-phase-and-state.html
Ehlers, EG and Potter, S. (2019, November 14). phase – Binary systems . Encyclopedia Britannica. https://www.britannica.com/science/phase-state-of-matter/Binary-systems
Phase of Matter and State of Matter . (2011, June 15). Difference Between. http://www.differencebetween.net/science/difference-between-phase-of-matter-and-state-of-matter/
Silica and health. (2019). crystalline silica . SCR web portal. https://www.siliceysalud.es/index.php/el-polvo-y-la-scr/la-silice/silice-cristalina/
Vatalis, Konstantinos & Charalambides, George & Benetis, Nikolas-Plutarch. (2015). Market of High Purity Quartz Innovative Applications. Proceded Economics and Finance. 24. 734-742. https://www.researchgate.net/figure/Phase-diagram-of-silica_fig1_283954321
