1. Ch 16 Thermal Energy and Heat

2. 16.1 Thermal Energy and Matter
In the 1700’s scientists thought heat was a fluid called a caloric that flowed between objects.
In 1798, the scientist Count Rumford concluded, from his observations, that heat could not be a kind of matter but instead was related to the motion of objects

4. Work and Heat
Recall… some of the work done by machines is lost due to friction, which causes moving parts to heat up
Heat = the transfer of thermal energy from one object to another because of a temperature difference

5. Heat flows spontaneously from hot objects to cold objects

7. Temperature
Temperature = a measure of how hot or cold an object is compared to a reference point. Such as the freezing and boiling pt of water.

8. Temperature is related to the average kinetic energy of the particles in an object due their random motions

10. Thermal Energy
Recall…
Thermal Energy = the total potential and kinetic energy of all the particles in an object
Thermal energy depends on the mass, temp, and phase of an object

11. Thermal energy, unlike temp, depends on mass
Ex: a cup of tea vs a teapot full of tea at 98º
Both have the same temp but the teapot has more particles = more thermal energy

13. Thermal Expansion & Contraction
Thermal expansion = occurs when particles of matter move farther apart as temp increases
Gases expand more than liquids and liquids more than solids

14. Ex: this is how thermometers work

17. Specific Heat
Specific Heat = the amount of heat needed to raise the temp of one gram of material by one degree Celsius
Units = J/g•Cº

18. The lower a material’s specific heat, the more its temp rises when a given amount of energy is absorbed by a given mass
Ex: water = 4.18, air = 1.01
Ex: water and alcohol

19. 16.2 Heat and Thermodynamics
When you take cookies out of a hot oven, why aren’t you burned by the hot air but would be burned by touching the metal rack?

20. Air is not a good conductor of heat while metal is

21. Conduction
Conduction = the transfer of thermal energy with no overall transfer of matter
Conduction occurs within a material or between materials that are touching
Collisions between particles transfer thermal energy

23. Conduction in gases is slower than in liquids and solids because the particles are farther apart
In solids, conduction occurs as particles vibrate in place and in metals conduction is faster because of the free electrons that collide and transfer heat

24. Thermal conductor = a material that conducts heat well
Ex: metals

25. Thermal insulators = a material that conducts heat poorly
Ex: air, plastics, foam, wool, wood

27. Convection
Convection = the transfer of thermal energy when particles of a fluid move from place to place
Ex: air circulating in an oven creates convection currents

28. Convection currents are important in many natural cycles: ocean currents, weather systems, movement of hot rock in Earth’s interior

30. All objects radiate heat energy.
Radiation
Radiation = the transfer of thermal energy by waves moving through space
All objects radiate heat energy.

34. Thermodynamics
Thermodynamics = the study of conversions between heat and other forms of energy

35. First Law of Thermodynamics = energy is conserved

37. Second Law of Thermodynamics = thermal energy can flow from colder to hotter objects only if work is done on the system
Ex: refrigerators must do work to transfer thermal energy from the cold food compartment to the warm room

39. Third Law of Thermodynamics = absolute zero cannot be reached

40. Scientists have gotten close…within 3 billionths of a kelvin above absolute zero