| Term | Definition |
| Fluid | A substance that can flow and take the shape of its container. |
| Freezing Point | The point in temperature by which liquid particles become solid particles. |
| Surface Tension | A force that pulls all large particles in a solvent together to make the smallest possible surface area. |
| Vaporization | The process by which liquid particles become gas particles. |
| Melting Point | The point in temperature by which solid particles become liquid particles. |
| Equilibrium | A dynamic condition in which two opposing changes occur at equal rates in a closed system. |
| Phase | Any part of a system that has uniform composition and properties. |
| Condensation | The process by which gas particles become liquid particles. |
| Le Chatelier's Principle | When a system at equilibrium is disturbed by application of a stress, it attains a new equilibrium position that minimizes the stress. |
| Volatile Liquid | A liquid that evaporates readily. |
| Boiling Point | The point in temperature in which liquid particles become gas particles. |
| Sublimination | The process of solid particles becoming gas particles. |
| Deposition | The process of gas particles becoming solid particles. |
| Molar Heat of Fusion | The amount of heat needed to vaporize one mole of liquid at its boiling point. |
| Phase Diagram | A graph of pressure versus temperature that shows the conditions under which the phases of a substance exist. |
| Critical Temperature | The temperature above which a substance cannot exist in a liquid state. |
| Critical Pressure | The lowest pressure at which a substance can exist as a liquid at the critical temperature. |