The Kinetic Molecular Theory

1. The Kinetic Molecular Theory States of Matter—Gases, Liquids and Solids

2. The Kinetic Molecular Theory The theory of moving molecules -Use to explain the properties of solids, liquids, and gases in terms of the energy of particles and the forces that act between them

3. The Kinetic Molecular Theory Major points: Supports the concept of an ideal gas… • An ideal gas is one that perfectly fits all the assumptions of the kinetic-molecular theory. • Do not actually exist—in theory this is how they would behave:

4. The Kinetic Molecular Theory 1. Gases consist of large numbers of tiny particles that are far apart relative to their size. 2. Collisions between gas particles and between particles and container walls are elastic collisions. Elastic collisions one in which there is no net loss of total kinetic energy. 3. Gas particles are in continuous, rapid, random motion. They possess kinetic energy, the energy of motion.

5. 4. There are no attractive forces between molecules (under normal conditions of temperature and pressure) 5. All gases at the same temperature have the same average kinetic energy of particles. Ke = ½ mv2 Ke = the kinetic energy m = mass v = the velocity

6. The Kinetic Molecular Theory • Applies only to ideal gases • Most gases behave like an ideal gas under normal conditions • Gases with little attraction between molecules…He/H2/N2 • Real gases • Deviate from ideal behavior • Due to intermolecular interaction (H2O, NH3) • High pressure • Low temperature

7. The Kinetic Theory and Changes of State • Gases—Attractions are insignificant • Liquids—Attractions are more important leading to a more ordered state • Solids –Attractions are most important with an ordered state

8. Kinetic Molecular Theory and Changes of State Solids, liquids and gases can undergo various changes in processes that are either endothermic or exothermic

9. Kinetic Molecular Theory and Changes of State

10. Kinetic Molecular Theory and Changes of State • The amount of heat energy required to melt one mole of a solid at the solid’s melting point is the solid’s molar enthalpy of fusion. • DHf • Energy absorbed represents potential energy • For water it is 6.009kJ/mol • Xj/g =6.009kJ/M x 1M/18g x 1000J/1kJ • = 333.8 j/g

11. Kinetic Molecular Theory and Changes of State • The amount of heat energy required to vaporize one mole of a liquid at the liquid’s boiling point is the liquid’s molar enthalpy of vaporization. • DHv • Energy absorbed represents potential energy • For water it is 40.79kJ/mol • Xj/g =40.79J/M x 1M/18g x 1000J/1kJ • = 2266 j/g

12. Solids and the Kinetic Molecular theory (10.4) • Properties: Dominated by the fact that • Closely packed particles • Relatively fixed positions • Highest intermolecular or interatomic attractions • Properties are • Definite shape and volume • Definite melting point • High density and incompressibility • Low rate of diffusion

13. Solid structure Solids may be crystalline Solids may be amorphous Crystals in which particles are arranged in a regular repeating pattern Particles are randomly arranged

14. Solid structure Crystals • Total 3-D arrangement of particles is the crystal structure • CUBIC • BODY CENTERED CUBIC • TETRGONAL • HEXAGONAL • TRIGONAL • MONO

15. 4-Classes of Crystalline Solids Ionic --Ions Hard and Britle Covalent Network Network of molecules Quartz (SiO) Diamond Metallic Crystals Free moving e- Covalent Molecular Crystals Weak…. Water, dry ice

16. Amorphous solids Without shape No regular pattern • Glasses • Plastics

17. Kinetic Molecular Theory and Changes of State (Water- 10.5) • Compared to other substances water has a high specific heat. • Water has very strong intermolecular bonding • Hydrogen bonds between highly polar molecules

18. Changes of State are Shown in Phase Diagrams • Changes of phase are depicted in phase diagrams • Show the relationship between state of matter, temperature and pressure

19. Changes of State Shown in Phase Diagrams Phase diagrams define: • Triple point=the T/P conditions at which all three phases coexist • Critical point = Critical temp and press • Critical temp = temp above which the substance cannot exist as a liquid • Critical press= lowest pressure at which the substance can exist as a liquid at the critical temperature

20. Phase Diagram of Water • Interesting points • AD—Ice and vapor in equilibrium • AC– Liquid and vapor in equilibrium • AB—Ice and liquid in equilibrium. Note an increase in pressure lowers melting point • nbp=normal boiling pt • mp =melting point • Critical temp =373.99

21. Phase Diagram of Carbon Dioxide • Note the following: • Very different temp and pressure compared to water’s diagram • Liquid is only possible at high pressure • At normal room conditions CO2 only exists as a gas

22. Phase Change vs Temperature change in a single phase • Melting/Fusion • …Molar heat of fusion • 6.009 kJ/mol • Vaporizing • Molar hear of vaporization • 40.79kJ/mol • Raising the temperature of a homogeneous material • Specific heat

23. Phase Change • How much energy is absorbed when 47g of ice melts? (at STP) • Energy =47g x1 mol x 6.009kJ 18g 1 mol = 15.7 kJ

24. Phase Change • How much energy is absorbed when 47g of water vaporizes? (at STP) • Energy =47g x1 mol x 40.79kJ 18g 1 mol = 106 kJ (vs 15.7 kJ—gases have a higher energy content)

25. Phase Change • What mass of steam is required to release 4.97 x 105kJ of energy when it condenses? • grams =4.97 x 105kJ x 1mol x 18g 40.79kJ 1 mol = 2.19 x 105 g

26. Temperature change in a single phase • Specific heat of water , Cp • Definition… the quantity of heat (q) required to raise 1 gram of water 1oC at a constant pressure. • Value will vary for each substance

27. Temperature change in a single phase • Quantity of energy transferred as heat while a temperature change occurs depends on • The nature of the substance • The mass of the material • The size of the temperature change. • Water has a high specific heat • Metals have low specific heat • Units = J/(g x oC)

28. Temperature change in a single phase • Specific heat of water (l) = 4.18 J/goC • Specific heat of water (s) = 2.06 • Specific heat of water (g) = 1.87 • Specific heat of ethanol (g) = 1.42 • Specific heat of ethanol (l) = 2.44 • Specific heat of mercury (l) = 0.140 • Specific heat of copper (s) = 0.385 • Specific heat of lead (s) = 0.129 • Specific heat of aluminum (s) = 0.897