Phase Transition and States of Matter

The activity of a substance changing from one state to another is called phase transition. Any element or substance can transition from one stage to the next at a specific pressure and temperature combination. For example, when water boils, it changes from a liquid to a gas. In all of these phases, the empirical formula is merely a normal function with continuous fluctuations. Except for compounds migrating from one phase to the next, they change their function abruptly. The liquid, solid and gas phases will be discussed in this chapter.

States of matter

Another method for learning phase transition is to link them to the initial state of matter:

• Solids may either melt or sublimate into liquids or gases.
• A liquid can either freeze to become a solid or evaporate to form a gas.
• A gas can freeze into a liquid, settle in a solid, or ionise into plasma.
• Plasma is a gas that may deionise or reunite to produce another gas. Remember that plasma is similar to a gas, except that the particles are wider apart and ionised.

Why do phase changes occur?

Most phase transitions are caused by a shift in the system’s energy. Temperature increases the kinetic energy of atoms and molecules, allowing them to break bonds and drift apart. Similarly, lowering the temperature causes particles to slow down and make it simpler to form a hard structure. Particles are pushed together by increasing pressure, whereas moving apart is made possible by reducing pressure.

A phase diagram indicates the state of matter of any substance at a given temperature and pressure. Plasma is formed when an ionised material becomes ionised. As a result, while raising temperature can cause ions to form, reducing pressure, even a vacuum, does not always cause plasma to develop.

Factors that affect the phase transition

• Temperature: Temperature can alter the phase of a component. Placing water in a freezer to turn it into ice is a frequent example. Because the system’s pressure remains constant, this form of phase shift is known as an isobaric cycle.

• Pressure: Pressure may be used to shift the phase of material as well. The pressure will rise as the piston tries to press the liquid till its melting point is achieved. After that, the liquid will solidify. It is an example of an isothermal process in which the temperature remains constant while the pressure changes.

Types of change of state 

A phase transition occurs at a specific temperature for every given pressure, frequently followed by heat emission and absorption, as well as a change in size and concentration. There are many states:

• Freezing

Freezing is the transformation of the physical state from liquid to solid. This method is used in labs to preserve vegetables (preserved food) and animal products.

• Boiling

Boiling is the method of changing a substance’s liquid phase into its vapour form.

• Condensation

The process through which an item changes its physical state from gas to liquid is called condensation. When it comes to a solution, there are two components: a solute and a solvent. This method aids in separating these opposites.

• Melting

Melting transforms the material from its solid to a liquid state. In most cases, it absorbs heat energy from the surroundings during the process.

• Sublimation

The transformation of a matter from solid to vapour is known as sublimation. The solid and gaseous phases coexist in thermal balance throughout the sublimation phase.

What is latent heat?

The latent heat of the material for the process is the amount of heat absorbed or transmitted per unit mass throughout the transition of the material. The formula is:

Q = mL

where L represents the latent heat.

Latent heat is also called Heat of Transformation. Its unit is cal/gm or J/kg.

Latent heat of fusion

When solids are heated, their temperature rises until they reach their melting point, at which point they begin to change. Additional heat energy has little effect on the temperature once the melting point has been achieved; instead, it provides energy for the phase transition from solid to liquid, known as melting. The Latent Heat of Fusion symbol Lf describes the solid-liquid transition. The equation that describes the melting process is Q=mLf.

Latent heat of vaporisation

The heat of vaporisation is the energy necessary to convert one mole of liquid to its boiling point at standard atmospheric pressure. The excess heat is required to transition a substance’s phase from solid to liquid at its melting temperature or from liquid to gaseous at its boiling temperature. Only once the temperature of the item reaches one of these stages does it vaporise. The latent heat of vaporisation (or enthalpy of vaporisation) is used here; however, the notion is the same as the latent heat of fusion. The Latent Heat of Vaporisation (Lv) symbolises liquid-gas transition, the equation is: Q=mLv