The diagram that shows molecules in both the liquid phase and the gas phase is one that represents conditions along the liquid-gas phase boundary or equilibrium line in a phase diagram. At points along this line, liquid and gas phases coexist in equilibrium, meaning molecules exist in both phases simultaneously. Explanation:
- A phase diagram plots pressure versus temperature and shows regions where solid, liquid, and gas phases are stable
- The lines (phase boundaries) on the diagram represent conditions where two phases coexist in equilibrium.
- The line separating the liquid and gas phases (often called the vaporization or boiling curve) shows the temperature and pressure at which liquid and gas coexist
- At any point on this liquid-gas boundary, molecules are present in both the liquid phase and the gas phase simultaneously.
- For example, water at 100°C and 1 atm pressure is at the boiling point where liquid water and water vapor coexist
Therefore, the correct diagram would be one that depicts molecules clustered closely together (liquid) and molecules more spread out (gas) in the same image, representing coexistence at the liquid-gas equilibrium line. If you have multiple diagrams to choose from, select the one illustrating molecules in a dense arrangement (liquid) alongside molecules spread far apart (gas), corresponding to conditions on the liquid-gas phase boundary of a phase diagram.
