1. Changes of State Solid to Liquid to Gas and Back

2. Introduction The change of state of a substance is a physical change - not a chemical change. We have already talked about... condensation (gas to liquid) boiling (liquid to gas) melting (solid to liquid) freezing (liquid to solid)

3. Introduction There is one more set of changes we need to consider. sublimation (solid to gas) and condensation (gas to liquid)

4. Sublimation Sublimation is the change of phase from a solid directly to a gas. There is no intermediate liquid phase. Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature. Sublimation commonly occurs in... dry ice solid air freshener

5. Condensation Condensation occurs when gas particles... encounter a solid of the same material... are attracted to the particles in the solid... and become a part of the solid. This means that solids and gases may be in equilibrium by condensation and sublimation.

6. Summary of Phase Changes Solid Liquid Gas Condensation Boiling Condensation Sublimation Melting Freezing

7. Phase Diagrams The relationships between the solid, liquid, and gas phases of a substance in a sealed container can be represented by a single graph called a phase diagram. We plot the pressure versus the temperature and put the various phases on the diagram. The conditions of pressure and temperature at which two phases exist in equilibrium are indicated by a line separating the two phases.

8. Phase Diagrams For example, the phase diagram for water looks like: pressure (kPa) temperature (°C) Solid Liquid Vapor

9. Phase Diagrams The triple point is where all three phases exist together. pressure (kPa) temperature (°C) Solid Liquid Vapor Triple Point

10. Phase Diagrams The triple point is 0.61 kPa at 0.016°C. pressure (kPa) temperature (°C) Solid Liquid Vapor Triple Point 0.61 kPa 0.016°C

11. Phase Diagrams The critical point is the highest temperature a substance can be a liquid pressure (kPa) temperature (°C) Solid Liquid Vapor Critical Point

12. Phase Diagrams The critical point of water occurs at 374°C and 22,064 kPa. pressure (kPa) temperature (°C) Solid Liquid Vapor Critical Point 22,064 kPa 374°C

13. Phase Diagrams At any given pressure, the temperature where we go from solid to liquid is the melting point. pressure (kPa) temperature (°C) Solid Liquid Vapor melting point

14. Phase Diagrams At any given pressure, the temperature where we go from liquid to vapor is the boiling point. pressure (kPa) temperature (°C) Solid Liquid Vapor boiling point

15. Phase Diagrams The normal melting point and boiling point occurs at 101.3 kPa. pressure (kPa) temperature (°C) Solid Liquid Vapor 101.3 kPa 0°C 100°C

16. Phase Diagrams The phase diagram of water is unlike most phase diagrams. In water, as the pressure increases, the melting point decreases.

17. Phase Diagrams Phase diagram of water pressure (kPa) temperature (°C) Solid Liquid Vapor melting point

18. Phase Diagrams Phase diagram of water pressure (kPa) temperature (°C) Solid Liquid Vapor melting point

19. Phase Diagrams The phase diagram of water is unlike most phase diagrams. In water, as the pressure increases, the melting point decreases. In almost all other systems, as the pressure increases, the melting point increases.

20. Phase Diagrams Phase diagram of something other than water pressure (kPa) temperature (°C) Solid Liquid Vapor melting point

21. Phase Diagrams Phase diagram of something other than water pressure (kPa) temperature (°C) Solid Liquid Vapor melting point

22. Phase Diagrams The phase diagram of water is unlike most phase diagrams. In water, as the pressure increases, the melting point decreases. In almost all other systems, as the pressure increases, the melting point increases. This is not the last time we will see that water behaves differently from most other compounds.

23. Summary The phase changes from solid are.. sublimation (to gas) and melting (to liquid) The phase changes from liquid are... boiling (to gas) and freezing (to solid) The phase changes from gas are... condensation (to liquid or solid)

24. Summary The relationships between the solid, liquid, and gas phases of a substance in a sealed container can be represented by a single graph called a phase diagram. The triple point is where all three phases exist together. The critical point is the highest temperature a substance can be a liquid. At any given pressure, the temperature where we go from solid to liquid is the melting point and where we go from liquid to gas is the boiling point.