What Is a Phase in Chemistry? Types, Examples & Importance
Whenever we discuss thermodynamics within the realms of Chemistry, the prospect of “phase” plays a significant role. In essence, the idea of a phase of a matter can be understood via the changes in their state that occur with differences in their surrounding temperatures and other conditions. However, such differences in the state of matter do not alter the chemical composition of the matter. To put it simply, the phase state of matter is a homogenous quantity, meaning it is constant in its chemical composition.
States of Matter Diagram
As most know, the three fundamental states of matter that are the most prevalent in our day to day lives are- Solid, Liquid and Gas or Vapour. The reason why these three are the most prevalent forms of thermodynamic phases is that they are the three phases that we are the most accustomed with. We have seen how water exists in its liquid form in lakes and oceans, whereas it exists in its solid form in icecaps and also, how it exists in its gaseous form when water is boiled on the stove. Thus, we are aware of the three primary phases of matter. However, the prospect of phase within the context of matter and its states is not limited to the three aforementioned states only. Other phases that exist, or are at least, considered, include- Amorphous, Colloid, Crystalline, Plasma and Glassy phases. Out of these, the phase catering to the Plasma state is considered the most prevalent.
In the thermodynamic phase of Plasma, the number of charged particles that comprise within the matter become roughly equal in number, which leads to the ionization of the gas of the matter since both the positively and the negatively charged particles become equal in number. Therefore, the state of Plasma is often considered the fourth phase of matter, after the solid, liquid and gaseous phases. The provided diagram can be referred to for further clarification.
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What is Phase in Chemistry
As has been discussed so far, the idea that is emblematic of the thermodynamic states of matter is largely relevant to the field of Chemistry, as well as that of Physics. Since these two fields are cut from the same fabric of Science, it is incredibly difficult to look at the subject of phase through the single lens of either of the two fields. Therefore, with regards to the aspect of phase in Chemistry, it is reasonable to state that, although the idea catering to the implementation of matter and its states falls primarily in the realm of Chemistry, the significance of Physics on the same idea cannot be discounted.
Therefore, to elaborate on the idea of the study of phases of matter in Chemistry, as we have discussed thus far, the phase definition Chemistry refers to the thermodynamic states of matter that are homogeneous in nature, where a matter solidifies, liquifies or evaporates with regards to the changes in its surrounding temperature and other influencing factors. Therefore, as can be inferred, the definition of Phase in the field of Chemistry remains the same as that of the Physical field.
Phases of Matter
Since the three primary types of phases within the context of any matter are- Solid, Liquid and Gas, as has been mentioned earlier, it is important to consider the prospect of phase change. By its definition, the concept of phase change occurs when a matter goes through an alteration in its form and enters another form. For instance, when we freeze water in the freezer, it goes from being in the liquid phase to being in the solid phase, thereby, a phase change occurs in the water.
Now, to answer the question, “What is phase in thermodynamics?”, we must consider the various phases of matter and how they are defined.
Solid: In this state of matter, there is a decrease in the atom energy, leading to the formation of a three- dimensional structure. For example, a cube of ice.
Liquid: In this state of matter, the structure of the matter is malleable, i.e., it takes the form of the vessel that it is poured inside of. For example, water in a jar.
Gas: In this state of matter, the structure of the matter is gaseous, meaning it cannot hold any particular shape or structure. For example, the vapor from boiling water.
Did You Know?
Gases are able to fill up any container as long as it is closed and has a volume. This is why gases are used to fill balloons of various shapes and sizes, instead of a liquid.
The molecules of gases move chaotically in vast numbers.
The idea of Phase Change was proposed by J. Willard Gibbs in 1876.
FAQs on Phases in Chemistry: Explained with Diagrams and Facts
1. What are the common phases of matter explained in chemistry?
In chemistry, matter primarily exists in four phases or states:
- Solid: Particles are tightly packed in a fixed structure with definite shape and volume.
- Liquid: Particles are close together but can move past one another, having a definite volume but no fixed shape.
- Gas: Particles are far apart and move randomly, having no fixed shape or volume.
- Plasma: A high-energy state where atoms are ionised, consisting of a mixture of electrons and positive ions. It is the most abundant state of matter in the universe.
2. What is a phase change and what causes it to occur?
A phase change, or phase transition, is the transformation of a substance from one physical state (like solid, liquid, or gas) to another. These changes are primarily caused by the addition or removal of energy, usually in the form of heat, at a specific temperature and pressure. For instance, adding heat can cause a solid to melt into a liquid, while removing heat can cause a gas to condense into a liquid.
3. What is a phase diagram and what key information does it provide?
A phase diagram is a graphical representation that shows the conditions of temperature (usually on the x-axis) and pressure (on the y-axis) under which a substance exists as a solid, liquid, or gas. It is important because it allows chemists and scientists to predict the phase of a substance at any given temperature and pressure and understand the boundaries where phase transitions occur.
4. What are the different types of phase transitions between states of matter?
There are six main types of phase transitions that describe the movement between the three primary states of matter:
- Melting (Fusion): The transition from solid to liquid.
- Freezing: The transition from liquid to solid.
- Vaporisation (Boiling/Evaporation): The transition from liquid to gas.
- Condensation: The transition from gas to liquid.
- Sublimation: The transition directly from solid to gas, bypassing the liquid phase.
- Deposition: The transition directly from gas to solid.
5. What is the significance of the triple point and the critical point on a phase diagram?
The triple point and critical point are two crucial coordinates on a phase diagram.
- The triple point is the specific temperature and pressure at which the solid, liquid, and gaseous phases of a substance can all exist simultaneously in equilibrium.
- The critical point represents the temperature and pressure above which the distinction between the liquid and gas phases disappears. Beyond this point, the substance exists as a supercritical fluid, which has properties of both a liquid and a gas.
6. How does the phase diagram of water show that ice is less dense than liquid water?
The phase diagram of water has a unique feature: the boundary line between the solid (ice) and liquid phases has a negative slope. This means that as pressure increases, the melting point of ice decreases. This unusual behaviour demonstrates that ice is less dense than liquid water. For most other substances, increasing pressure favours the denser, solid state, but for water, pressure favours the denser, liquid state, causing ice to melt.
7. Why is it incorrect to describe plasma as just a very hot gas?
While plasma is formed by heating a gas to very high temperatures, it is a distinct state of matter, not just a hot gas. The key difference is that the immense energy in plasma causes atoms to lose their electrons, creating a mixture of positively charged ions and free electrons. This ionisation makes plasma electrically conductive and highly responsive to magnetic fields, properties that neutral gases do not possess.
