States of Matter - Changes of state

Kinetic Molecular Theory: Matter is composed of particles in constant motion. The average kinetic energy of these particles is directly proportional to the absolute temperature $T$ in Kelvin ($K$).

Melting and Freezing: Melting is an endothermic process where a solid turns into a liquid at a specific melting point. The energy supplied is used to overcome the lattice forces, represented by the enthalpy of fusion $\Delta H_{fus}$.

Boiling vs. Evaporation: Boiling occurs throughout the liquid at a fixed temperature (boiling point) where vapor pressure equals atmospheric pressure. Evaporation occurs only at the surface and can happen at any temperature below the boiling point.

Heating Curves: During a change of state (e.g., $S \rightarrow L$ or $L \rightarrow G$), the temperature remains constant. This plateau occurs because the energy absorbed is used to break intermolecular forces ($IMF$) rather than increasing the kinetic energy of the particles.

Sublimation and Deposition: Sublimation is the direct transition from solid to gas (e.g., $CO_2(s) \rightarrow CO_2(g)$ or $I_2(s) \rightarrow I_2(g)$). Deposition is the reverse process.

Condensation: An exothermic process where gas particles lose energy and move closer together to form a liquid, releasing the enthalpy of vaporization $\Delta H_{vap}$.