1. Thermal Energy and Heat
Chapter 16
Thermal Energy and Heat

2. 16.1 Thermal Energy and Matter
Thermal Energy and Heat
16.1 Thermal Energy and Matter

3. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Work and Heat
Heat is the transfer of thermal energy from one object to another because of a difference in temperature.
Heat flows spontaneously from hot objects to cold objects.

4. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Temperature
Temperature is a measure of how hot or how cold an object is compared to a reference point.
Temperature is related to the average kinetic energy of the particles in an object due to their random motions through space.

5. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
As an object heats up, its particles move faster, on average.
As a result, the average KE of the particles and the temperature increase.

6. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Why does heat flow from high to low temperature?
Heat flow is by the transfer of energy in collisions.

7. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
High-energy particles lose energy, and low-energy particles gain energy during collisions.
The collisions transfer thermal energy from hot to cold objects.

8. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Thermal Energy
Thermal energy is the total potential and kinetic energy of all the particles in an object.
Thermal energy depends on mass, temperature, and phase of an object.

9. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Figure 2 shows the particles in a cup of hot tea and in a pitcher of lemonade.
The tea is at a higher temperature, but the pitcher of lemonade has many more particles.
The pitcher of lemonade actually has more thermal energy.

10. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat

11. Thermal Contraction and Expansion
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Thermal Contraction and Expansion
Thermal expansion is an increase in the volume of a material due to a increase in temperature.
Thermal expansion occurs when particles of matter move farther apart as temperature increases.

12. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Gases expand more than liquids and liquids usually expand more than solids.
A gas expands more easily because the forces of attraction in a gas are weaker.

13. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Specific Heat
Specific heat is the amount of heat needed to raise the temperature of one gram of a material by one degree Celsius.
The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass.
Specific heat is measured in joules per gram per degree Celsius (J/goC).

14. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
The heat (Q) absorbed by a material equals the product of the mass, the specific heat, and the change in temperature.
Q=mc∆t

15. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat

16. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Specific Heat

17. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Specific Heat

18. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Specific Heat

19. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Specific Heat

20. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Q=mc∆t
m=Q/c∆t
c=Q/m∆t
∆t=Q/mc

21. Measuring Heat Changes
16.1 Thermal Energy and Matter
Thermal Energy and Heat
Measuring Heat Changes
A calorimeter is an instrument used to measure changes in thermal energy.
A calorimeter uses the principle that heat flows from hotter object to a colder object until both reach the same temperature.

22. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat
According to the law of conservation of energy, the thermal energy released by a test sample is equal to the thermal energy absorbed by its surroundings.
Figure 4 shows how a calorimeter can be used to measure specific heat.

23. Thermal Energy and Heat
16.1 Thermal Energy and Matter
Thermal Energy and Heat

24. 16.2 Heat and Thermodynamics
Thermal Energy and Heat
16.2 Heat and Thermodynamics

25. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat

26. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Conduction
Conduction is the transfer of thermal energy with no overall transfer of matter.
Conduction occurs within a material or between materials that are touching.
In conduction, collisions between particles transfer thermal energy.

27. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often.
In metals, conduction is faster because the electrons are free to move about.

28. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Thermal Conductors
A thermal conductor is a material that conducts thermal energy well.

29. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Thermal Insulators
A material that conducts thermal energy poorly is called a thermal insulator.
Air is a very good insulator.

30. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Convection
Convection is the transfer of thermal energy when particles in a fluid move from one place to another.
A convection current occurs when a fluid circulates in a loop as it alternately heats up and cools down.

31. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Radiation
Radiation is the transfer of energy by waves moving through space.
All objects radiate energy.
As an object’s temperature increases, the rate at which it radiates energy increases.

32. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Thermodynamics
The study of conversions between thermal energy and other forms of energy is called thermodynamics.

33. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Joule carefully measured the energy changes in a system which included a falling weight that turned a paddle wheel in a container of water.

34. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat

35. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat

36. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
As the weight fell, the paddle churned a known mass of water.
The water heated up due to friction from the paddle.

37. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Joule found the work done by the falling weight almost exactly equaled the thermal energy gained by the water.
The law of conservation applied to work, heat, and thermal energy.

38. First Law of Thermodynamics
16.2 Heat and Thermodynamics
Thermal Energy and Heat
First Law of Thermodynamics
The first law of thermodynamics states that energy is conserved.
If energy is added to a system, it can either increase the thermal energy of the system or do work on the system.

39. Second Law of Thermodynamics
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Second Law of Thermodynamics
The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects only if work is done on the system.
A heat engine is any device that converts heat into work.

40. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
One consequence of the second law is that the efficiency of a heat engine is always less than 100%.

41. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
The best an engine can do is to convert most of the input energy into useful work.
Thermal energy that is not converted into work is called waste heat.
A heat engine can do work only if some waste heat flows to a colder environment outside the engine.

42. Thermal Energy and Heat
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Spontaneous changes will always make a system less orderly, unless work is done on the system.
Disorder in the universe is always increasing.

43. Third Law of Thermodynamics
16.2 Heat and Thermodynamics
Thermal Energy and Heat
Third Law of Thermodynamics
The third law of thermodynamics states that absolute zero cannot be reached.