Phase Changes: Melting, Boiling, Sublimation, and Condensation - SS1 Chemistry Lesson Note

Phase changes, also known as phase transitions, are physical transformations that occur when matter transitions between different states. The most common phase changes include melting, boiling (or vaporisation), sublimation, and condensation. Let us delve into the intricacies of these phase changes, their underlying principles, and their significance in various scientific disciplines:

 

Melting:

Melting, also known as fusion, is the phase change from a solid to a liquid state. It occurs when a substance absorbs enough heat energy to overcome the attractive forces between its particles. The temperature at which melting occurs is known as the melting point. During melting, the solid's particles gain enough energy to break free from their fixed positions, allowing them to move more freely. Examples of melting include the transformation of ice into water and the melting of wax when heated.

 

Boiling (Vaporization):

Boiling, or vaporisation, is the phase change from a liquid to a gas state. It occurs when a liquid is heated, and its vapour pressure becomes equal to the atmospheric pressure or the pressure applied to it. Boiling can happen at a specific temperature called the boiling point. During boiling, the liquid's particles gain enough energy to overcome the intermolecular forces holding them together and escape into the gas phase. The most common example of boiling is water boiling and transforming into steam.

 

Sublimation:

Sublimation is the phase change directly from a solid to a gas state, bypassing the liquid state. It occurs when the vapour pressure of a solid substance exceeds the atmospheric pressure without going through a liquid phase. Sublimation is an endothermic process, meaning it requires energy input. Examples of substances that undergo sublimation include dry ice (solid carbon dioxide) and mothballs (solid naphthalene).

 

Condensation:

Condensation is the phase change from a gas to a liquid state. It occurs when a gas loses energy and transitions to a liquid phase. Condensation typically happens when a gas is cooled or when the vapour pressure of the gas exceeds the saturation vapour pressure. When condensation occurs, the gas particles lose energy, come closer together, and form liquid droplets. Condensation is responsible for the formation of clouds, dew, and rain.

 

These phase changes have significant implications in various scientific disciplines:

 

-       Thermodynamics: The study of phase changes is essential in thermodynamics, as it helps understand energy transfer, heat exchange, and the behaviour of substances under different conditions.

 

-       Atmospheric Science: Phase changes play a crucial role in weather patterns, cloud formation, and precipitation. The condensation of water vapour in the atmosphere leads to the formation of clouds, rain, and snow.

 

-       Chemistry: Phase changes are fundamental to chemical reactions, as they influence the physical and chemical properties of substances. Understanding phase changes is vital for reaction kinetics, equilibrium, and material synthesis.

 

-       Materials Science: Phase changes are essential in materials science, as different phases of a material can exhibit distinct properties, such as electrical conductivity or mechanical strength. The ability to control phase transitions is crucial for developing new materials with desired properties.