Thermal Energy & Matter

1. Thermal Energy & Matter 16.1

2. Demonstration • Food Coloring and Water

3. What is Heat? • The transfer of thermal energy from one object to another because of a temperature difference • Flows spontaneously from hot objects to cold objects

4. Temperature • Related to the average kinetic energy of the particles in an object due to their random motions through space

5. Kinetic Theory of Matter • Matter is made up of particles (or atoms) that are in constant motion

6. HEAT UP COOL DOWN Particles move slower, average kinetic energy of all particles decreases • Particles gain kinetic energy, move faster, average kinetic energy of all particles increases

7. Dice Game • You are now a particle of matter…

8. Thermal Energy • The total potential and kinetic energy of all the particles in an object • Depends on the mass, temperature and phase (solid, liquid, or gas) of an object

9. Balloon Demonstration

10. Thermal Contraction • As temperature decreases, particles move more slowly • Slower moving particles have less average kinetic energy • This means that the particles collide less often and exert less force on one another

11. Can Demonstration

12. Thermal Expansion • Occurs when particles of matter move farther apart as temperature increases • Gases expand more than liquids • This is because the forces of attraction among particles in a gas are weaker • Liquids expand more than solids

15. Making Thermometers • Now, your group will make a thermometer using the materials provided in order to see thermal expansion and contraction first hand.

16. An Important Exception • Water • Water expands as it freezes, unlike most other substances • This is due to something called Hydrogen Bonding, which we will learn more about next semester • This has important corollaries in everyday life… Can you think of any?

19. Specific Heat • The amount of heat needed to raise the temperature of one gram of a material by one degree Celsius • The higher a material’s specific heat, the less its temperature rises when a given amount of energy is absorbed by a given mass

20. Different materials heat up at different rates!

21. Water • Water has a high specific heat • This means that it takes a lot of thermal energy to change temperature of water • Why? • Hydrogen Bonding (more to come next semester) • Consequences of Waters high specific heat? • Weather (daily and long term)

23. Measuring Heat Changes • Heat flows from hotter objects to cooler objects until both objects reach the same temperature • A calorimeter is a device that can be used to measure changes in thermal energy

24. Heat Transfer • Three Methods • Conduction • Convection • Radiation

25. Conduction • Transfer of thermal energy with no overall transfer of matter • Occurs within a material or between materials that are touching • Particles bump into one anther and transfer kinetic energy to one another

27. In which phase of matter does conduction occur most slowly? Why? Answer

28. Thermal Conductors • Material that conducts thermal energy well • Metals tend to be good conductors • Example: Pots, pans, & over racks are all made of metal • Thermal conductors don’t have to be “hot” • Tile vs. Wood • Tile feels colder because it transfers thermal energy rapidly away from your skin

29. Thermal Insulators • A material that transfers thermal energy poorly • Example: Wood, plastic • Air is a good insulator • Example: Double-paned windows have an air space between two sheets of glass; this slows conduction to reduce heat loss in the winter and to keep heat out during the summer • Other examples?

30. Convection • The transfer of thermal energy when particles of a fluid move from one place to another • Thermal energy is transferred by the mass movement of matter • Convection Current • Occurs when a fluid circulates in a loop as it alternately heats up and cools down • Important in natural cycles like ocean currents, weather systems and the movement of hot rock in Earth’s interior

33. Radiation • The transfer of energy by waves through empty space • How is radiation different than convection and conduction? • It does not require matter as a medium of transfer • Common Examples • The sun heats the earth • Heat lamps used in restaurants to keep food warm

34. Radiation (continued) • All objects radiate energy • As temperature of an object increases, the rate at which it radiates energy increases

37. Thermodynamics • The study of conversions between thermal energy and other forms of energy

38. First Law • Energy is always conserved • Energy can be converted into different forms, but it is never created nor destroyed

39. Second Law • Thermal energy can flow from colder objects to hotter objects ONLYif work is done on the system • Example: A refrigerator • A refrigerator moves heat thermal energy from the inside refrigeration compartment to outside of the refrigerator

40. Heat Engines • Any device that converts heat into work • In other words, a device that uses heat to “move” • No heat engine is 100% efficient • The heat engine does not convert all of the heat into work, some heat is lost to t he surrounding environment (called Waste Heat) • Fun Fact • The universe is continuously becoming less ordered due to wasted energy!

41. Third Law • Absolute Zero cannot be reached • Absolute Zero • 0 Kelvin, the theoretical lowest possible temperature • At this temp. all matter would stop moving (which means that the thermal energy of atoms would disappear!) • What is Absolute Zero?

42. Thermal Equilibrium • Higher temperature objects will transfer thermal energy to colder temperature objects • The objects will approach the same temperature, and then (in the absence of heat loss or gain from other objects) they will maintain a constant temperature • Example of Student Graph