Final answer:
The melting point and boiling point refer to temperatures at which a substance transitions between phases, such as solid to liquid, or liquid to gas, respectively. Density is a measure of mass per volume and is not a phase change. A phase change includes transitions like melting, freezing, evaporation, and condensation, and these changes are represented on a phase diagram, which includes the triple point.
Step-by-step explanation:
Difference Between Boiling Point, Melting Point, Density, and the 5 Phase Changes
The melting point is the temperature at which a substance transitions from a solid phase to a liquid phase, known also as melting. Conversely, the freezing point is the temperature at which a liquid becomes a solid, known as freezing. The boiling point is the temperature where a liquid changes to a gas, which is typically more rapid than evaporation and occurs throughout the liquid, not just at the surface; the reverse process is condensation. Density refers to the mass per unit volume of a substance and is an intrinsic property that does not change with the phase. Phase changes, or transitions, include melting (solid to liquid), freezing (liquid to solid), evaporation (liquid to gas), condensation (gas to liquid), and sublimation (solid to gas without passing through the liquid phase).
Phase changes are influenced by both temperature and pressure, which are depicted on a phase diagram; this diagram shows the conditions under which different phases coexist. The point where all three phases can coexist in equilibrium is called the triple point.