Chapter 9- The States of Matter

1. Chapter 9- The States of Matter • Gases indefinite volume and shape, low density. • Liquids definite volume, indefinite shape, and high density. • Solids definite volume and shape, high density • Solids and liquids have high densities because their molecules are close together.

2. Kinetic Theory l l are evidence of this. • Kinetic theory says that molecules are in constant motion. • Perfume molecules moving across the room

3. The Kinetic Theory of GasesMakes three assumptions about gases • A Gas is composed of particles • usually molecules or atoms • Considered to be hard spheres far enough apart that we can ignore their volume. • Between the molecules is empty space.

4. The particles are in constant random motion. • Move in straight lines until they bounce off each other or the walls. • All collisions are perfectly elastic

5. Kinetic Energy and Temperature • Temperature is a measure of the Average kinetic energy of the molecules of a substance. • Higher temperature faster molecules. • At absolute zero (0 K) all molecular motion would stop.

6. High temp. % of Molecules Low temp. • Kinetic Energy

7. High temp. Low temp. % of Molecules Few molecules have very high kinetic energy • Kinetic Energy

8. High temp. % of Molecules Low temp. Average kinetic energies are temperatures • Kinetic Energy

9. Temperature • The average kinetic energy is directly proportional to the temperature in Kelvin • If you double the temperature (in Kelvin) you double the average kinetic energy. • If you change the temperature from 300 K to 600 K the kinetic energy doubles.

10. Temperature • If you change the temperature from 300ºC to 600ºC the Kinetic energy doesn’t double. • 873 K is not twice 573 K

11. Liquids • Particles are in motion. • Attractive forces between molecules keep them close together. • These are called intermolecular forces. • Inter = between • Molecular = molecules

12. Breaking intermolecular forces. • Vaporization - the change from a liquid to a gas below its boiling point. • Evaporation - vaporization of an uncontained liquid ( no lid on the bottle ).

13. Evaporation • Molecules at the surface break away and become gas. • Only those with enough KE escape • Evaporation is a cooling process. • It requires heat. • Endothermic.

14. Condensation • Change from gas to liquid • Achieves a dynamic equilibrium with vaporization in a closed system. • What is a closed system? • A closed system means matter can’t go in or out. (put a cork in it) • What is • “dynamic equilibrium?”

15. Vaporization • Vaporization is an endothermic process - it requires heat. • Energy is required to overcome intermolecular forces • Why we sweat.

16. Energy needed to overcome intermolecular forces % of Molecules T1 Kinetic energy

17. % of Molecules • At higher temperature more molecules have enough energy • Higher vapor pressure. T2 Kinetic energy

18. Boiling • A liquid boils when the vapor pressure = the external pressure • Normal Boiling point is the temperature a substance boils at 1 atm pressure. • The temperature of a liquid can never rise above it’s boiling point.

19. Solids • Intermolecular forces are strong • Can only vibrate and revolve in place. • Particles are locked in place - don’t flow. • Melting point is the temperature where a solid turns into a liquid.

20. The melting point is the same as the freezing point. • When heated the particles vibrate more rapidly until they shake themselves free of each other. • Ionic solids have strong intermolecular forces so a high mp. • Molecular solids have weak intermolecular forces so a low mp.

21. Energy and Phase Change • Heat of vaporization energy required to change one gram of a substance from liquid to gas. • Heat of condensation energy released when one gram of a substance changes from gas to liquid.

22. Energy and Phase Change • Heat of fusion energy required to change one gram of a substance from solid to liquid. • Heat of solidification energy released when one gram of a substance changes from liquid to solid.

23. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Heat of Vaporization

24. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Heat of Fusion

25. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Steam Water Slope = Specific Heat Ice

26. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Both Water and Steam

27. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Ice and Water

28. Calcualting Energy • Three equations • Heat = specific heat x mass x DT • Heat = heat of fusion x mass • Heat = heat of vaporization x mass