Describe the phase changes of melting boiling s... - SS1 Chemistry States of Matter Question

Phase changes are physical transformations that occur when a substance transitions from one state of matter to another. Four common phase changes are melting, boiling (or vaporisation), sublimation, and condensation.

 

Melting:

Melting is the phase change from a solid to a liquid state. It occurs when a substance absorbs enough heat energy to overcome the forces holding its particles in a fixed lattice structure. As heat is added, the particles gain energy, increasing their vibrational motion and eventually breaking free from their fixed positions. The temperature at which melting occurs is called the melting point. During melting, there is an energy input without a change in temperature, as the absorbed heat energy is used to weaken the intermolecular forces.

 

Boiling (Vaporization):

Boiling, or vaporisation, is the phase change from a liquid to a gas state that occurs throughout the liquid, not just at the surface. It happens when a liquid is heated to its boiling point, and the vapour pressure of the liquid equals the atmospheric pressure. At the boiling point, the heat energy supplied is used to convert the liquid into gas, and the temperature remains constant until the phase change is complete. The process involves the breaking of intermolecular forces between liquid particles, allowing them to escape as gas particles.

 

Sublimation:

Sublimation is the phase change directly from a solid to a gas state without passing through the liquid phase. Certain substances, like dry ice (solid carbon dioxide), undergo sublimation under specific conditions of temperature and pressure. Sublimation occurs when the heat energy absorbed by the solid causes its particles to gain enough energy to overcome the intermolecular forces and transform directly into a gas. In sublimation, there is no intermediate liquid phase.

 

Condensation:

Condensation is the reverse of vaporisation and occurs when a gas or vapour changes into a liquid state. It happens when a gas loses heat energy to the surroundings, leading to a decrease in the average kinetic energy of the gas particles. As a result, the particles slow down and come closer together, forming intermolecular forces that allow them to transition into a liquid state. The temperature at which condensation occurs is called the dew point.