1. Unit 10 States of Matter and Gases

2. Phase Changes A phase change is a change in the state of matter During a phase change there is no change in temperature – the KE is used to spread or bring together the molecules of the substance During a phase change there is only a change in potential energy

3. Phase Changes Temperature - Measure of average kinetic energy - Doesn’t change during a phase change Energy causes molecules to spread out or come closer together

4. Phase Changes Solid becomes a liquid - Melting Point Liquid becomes a solid - Freezing Point Gas becomes a liquid - Condensation Point Liquid becomes a gas - Boiling Point

5. Phase Changes Melting and Freezing Points are the SAME TEMPERATURE Condensation and Boiling Points are the SAME TEMPERATURE

6. Phase Changes Normal Boiling Point - Boiling point of a substance at 1 atm - 1 atm = 760 Torr = 760 mm Hg = 101.3 kPa - Water is 100 0 C Normal Freezing Point - Freezing point of a substance at 1 atm - Water is 0 0 C

7. Heating Curves Heating Curve plot of temperature versus time for a substance - energy is added at a constant rate - X-axis can also be time

8. Heating Curves l Flat lines No change in temperature Phase changes 2 phases exist at the same time Change in potential energy Sloped lines Change in temp Change in kinetic energy

9. Phase Diagrams A phase diagram shows states of matter at different temperatures and pressure. Lines represent where the phase changes happen On lines – 2 phases exist

10. Phase Diagrams Triple point Where all 3 lines intersect All 3 phases exist at once Critical point Where gas/liquid line ends Supercritical fluid exists in region beyond point

11. Phase Diagrams Supercritical Fluid Has the density of a liquid, so it can dissolve things Behaves like a gas Used to extract chemicals/flavors (coffee, tea, spices)

12. Phase Diagrams

13. Intermolecular Forces 11.2 Intermolecular forces are attractive forces between molecules. Exist between separate molecules of a substance Weaker than intramolecular forces Affect melting point, boiling point, etc. Intramolecular forces hold atoms together in a molecule Occur between atoms inside a molecule Ex: bond energy for ionic and covalent bonds

14. Intermolecular Forces 1. Hydrogen Bond (strongest of all Intermolecular forces) 11.2 Hydrogen in a polar molecule attracted to a highly electronegative atom (O, N, F) in another. IT IS NOT AN ACTUAL BOND.

15. Hydrogen Bond 11.2 Intermolecular Forces

16. Types of Intermolecular Forces 2. Dipole-Dipole Forces Attractive forces between polar molecules Slightly pos. end of one attracts slightly neg. end of other. 11.2 Orientation of Polar Molecules in a Solid

17. Types of Intermolecular Forces 3. London Dispersion Forces – van der Walls forces (weakest) Attractive forces that are temporary dipoles in nonpolar molecules Momentary imbalance of electrons Affects all atoms Only forces in noble gases and nonpolar molecules 11.2

18. Types of Intermolecular Forces 3. London Dispersion Forces – van der Walls forces (weakest) 11.2

19. S O O What type(s) of intermolecular forces exist between each of the following molecules? HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules. CH 4 CH 4 is nonpolar: dispersion forces. SO 2 SO 2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO 2 molecules. 11.2