1. Chapters 13 & 17 Phases and Heat

2. Phases There are three phases, or states, that we will discuss  Solid  Liquid  Gas

3. Phases Solid (s)  form of matter that has a definite shape and definite volume. Liquid ( l )  form of matter that has a definite volume, indefinite shape, and flows. Gas (g)  form of matter that takes both the shape and volume of its container

4. Phases In most solids the particles are packed tightly together (regular geometric pattern) The particles in solids tend to vibrate around fixed points In liquids the particles have just enough space to slide past each other The particles in a gas are spread very far apart

5. Phase Changes When you heat a solid, the particles vibrate more rapidly, spreading apart enough to slide past each other (melting) When you heat a liquid the particles move around more rapidly Once they have enough energy to overcome the forces of attraction they spread far apart (vaporization)

6. Phase Changes Six Changes  Solid  LiquidMelting  Liquid  SolidFreezing  Liquid  GasVaporization  Gas  LiquidCondensation  Solid  GasSublimation  Gas  SolidDeposition

7. Phase Changes During any given phase change, both phases can exist together in equilibrium Example  At 0°C, water can exist in both the liquid and solid phases in equilibrium

8. Energy When energy is added to a reaction, or phase change, it is called Endothermic When energy is released during a reaction, or phase change, it is called Exothermic

9. Phase Changes Which phase changes are endothermic, requiring the addition of energy?  Melting  Vaporization  Sublimation

10. Phase Changes Which phase changes are exothermic, releasing energy?  Freezing  Condensation  Deposition

11. Short Cut S L g ExothermicEndothermic

13. Phase Diagram of CO 2

15. Energy What is energy?  Capacity to do work  Ability to do something Two main types  Kinetic  Potential

16. Types of Energy Kinetic Energy  Energy of motion  Related to the speed and mass of molecules Potential Energy  Stored energy

17. Temperature How is energy related to Temperature? What happens to a substance when you add energy?  Particles move faster  Temperature increases

18. Temperature Relationship between energy, particle speed, and temperature Temperature Definition  Average Kinetic Energy

19. Temperature Scales Kelvin (K) and Celsius (°C) scales Kelvin scale is called the absolute scale  Directly related to the kinetic energy of a substance Celsius scale is a relative scale  based on the boiling and freezing points of water

20. Temperature Conversion K = °C + 273

21. Pressure What is pressure? Physics – Force per unit area Chemistry – number of collisions between particles and container walls

22. Pressure Conversion 1 atm = 101.3 kPa

23. STP Standard Temperature and Pressure  Table A in Reference Tables 0°C, 273K 1 atm, 101.3kPa

25. Vapor Pressure Pressure exerted by vapor that has evaporated and remains above a liquid Related to temperature  As temperature increases, vapor pressure increases

26. Boiling vs. Evaporation Boiling  Vapor pressure equals external, or atmospheric pressure Evaporation  Some molecules gain enough energy to escape the liquid phase  At temp. less than boiling point

27. Normal Boiling Point Boiling Point at Standard Pressure 1 atm or 101.3 kPa

28. Table H Shows the relationship between temperature and vapor pressure for four specific substances

31. Thermochemistry Heat involved with chemical reactions and phase changes

32. Heat Energy transferred from one object to another, because of a temperature difference Measured in Joules (J) Heat flows from hot to cold

33. Heat Transfer Endothermic  Energy being added Exothermic  Energy being released

34. Conservation of Energy Energy can not be created or destroyed, only transferred or converted from one form to another. Energy lost by one object must be gained by another object or the environment  Heat Lost = Heat Gained

35. Example A chunk of iron at 80°C is dropped into a bucket of water at 20°C. What direction will heat flow?  From the iron to the water  Hot to cold

36. Example A chunk of iron at 80°C is dropped into a bucket of water at 20°C. What could be the final temperature, when they both come to equilibrium?  Between 20°C and 80°C

37. Heat Transfer What factors affect the amount of heat transferred?  Mass  Temperature difference between objects  Substance

38. Heat Transfer Specific Heat Capacity  Amount of energy needed to change the temperature of 1g of a substance by 1°C Unique for each phase of each substance

39. Heat Transfer Heat of Fusion  Amount of energy needed to melt (or freeze) 1 gram of a substance

40. Heat Transfer Heat of Vaporization  Amount of energy needed to vaporize (or condense) 1 gram of a substance  Heat of Vaporization > Heat of Fusion

42. Phase Change At what temperature does ice melt?  0°C At what temperature does water freeze?  0°C Melting point and freezing point are the same

43. Phase Change What happens to temperature during phase changes?  Temperature remains constant Temperature remains CONSTANT during a phase change

44. Phase Change If energy is being added, what kind of energy is it?  Energy being added is potential energy, not kinetic energy  Potential energy is being used to separate or spread the particles apart

45. Phase Change Which requires more energy melting or vaporization?  Vaporization Why?  Molecules are spread farther apart as a gas  It takes more energy to get gas particles spread apart

46. Heating (Cooling) Curves Shows relationship between temperature and time during constant heating or cooling. Also shows phases, and the phase changes between them.

47. Heating Curves Diagonal lines are phases Horizontal lines are phase changes Time (s) Temp (˚C) Gas Liquid Solid

48. Heating Curves Diagonal lines are phases Horizontal lines are phase changes Time (s) Temp (˚C) Vaporization Condensation Melting Freezing