1. Temperature, Heat, and the Thermal Behavior of Matter
Chapters 16, 17
Temperature, Heat, and the Thermal Behavior of Matter

2. Temperature
Thermodynamics – branch of physics studying thermal energy of systems
Temperature (T), a scalar – measure of the thermal (internal) energy of a system
SI unit: K (Kelvin)
Kelvin scale has a lower limit (absolute
zero) and has no upper limit
William Thomson
(Lord Kelvin) ( )

3. Kelvin scale
Kelvin scale is defined by the temperature of the triple point of pure water
Triple point – set of pressure and temperature values at which solid, liquid, and gas phases can coexist
International convention:
T of the triple point of water is

4. The zeroth law of thermodynamics
If two (or more) bodies in contact don’t change their internal energy with time, they are in thermal equilibrium
0th law of thermodynamics: if bodies are in thermal equilibrium, their temperatures are equal

5. Measuring temperature
Temperature measurement principle: if bodies A and B are each in thermal equilibrium with a third body C, then A and B are in thermal equilibrium with each other (and their temperatures are equal)
The standard temperature for the Kelvin scale is measured by the constant-volume gas thermometer

6. Constant-volume gas thermometer

7. Celsius and Fahrenheit scales
Celsius scale:
Fahrenheit scale:
Anders Cornelius
Celsius
( )
Gabriel Daniel
Fahrenheit
( )

8. Temperature and heat
Heat (Q): energy transferred between a system and its environment because of a temperature difference that exists between them
SI Unit: Joule
Alternative unit: calorie (cal):

9. Q Q Absorption of heat Specific heat (c): heat capacity per unit mass
Common states (phases) of matter: solid, liquid, gas
Latenet heat (L): the amount of energy per unit mass transferred during a phase change (boiling, condensation, melting, freezing, etc.) Q Q

10. Absorption of heat Q Q

11. Absorption of heat

12. Absorption of heat

13. Chapter 17
Problem 25
How much energy does it take to melt a 65-g ice cube?

14. Heat transfer mechanisms
Thermal conduction
Conduction rate:
Thermal resistance:
Conduction through a composite rod:
Thermal conductivity

15. Absorption of heat

16. Heat transfer mechanisms
Thermal radiation
Radiation rate:
Stefan-Boltzmann constant:
Absorption rate:
Emissivity
Josef Stefan
( )

17. Heat transfer mechanisms
Convection

18. Heat transfer mechanisms

19. Chapter 16
Problem 35
An oven loses energy at the rate of 14 W per °C temperature difference between its interior and the 20°C temperature of the kitchen. What average power must be supplied to maintain the oven at 180°C?

20. Avogadro’s number
Mole – amount of substance containing a number of atoms (molecules) equal to the number of atoms in a 12 g sample of 12C
This number is known as Avogadro’s number (NA):
NA = 6.02 x 1023 mol -1
The number of moles in a sample
N – total number of atoms (molecules)
m – total mass of a sample, m0 – mass of a single atom (molecule); M – molar mass
Amedeo Avogadro
( )

21. Ideal gases Ideal gas – a gas obeying the ideal gas law:
R – gas constant
R = 8.31 J/mol ∙ K
kB – Boltzmann constant
kB = 1.38 x 1023 J/K
Ludwig Eduard
Boltzmann
( )

22. Ideal gases The gas under consideration is a pure substance
All molecules are identical
Macroscopic properties of a gas: P, V, T
The number of molecules in the gas is large, and the average separation between the molecules is large compared with their dimensions – the molecules occupy a negligible volume within the container
The molecules obey Newton’s laws of motion, but as a whole they move randomly (any molecule can move in any direction with any speed)

23. Ideal gases
The molecules interact only by short-range forces during elastic collisions
The molecules make elastic collisions with the walls and these collisions lead to the macroscopic pressure on the walls of the container
At low pressures the behavior of molecular gases approximate that of ideal gases quite well

24. Ideal gases

25. Ideal gases
Root-mean-square (RMS) speed:

26. Translational kinetic energy
Average translational kinetic energy:
At a given temperature, ideal gas molecules have the same average translational kinetic energy
Temperature is proportional to the average translational kinetic energy of a gas

27. Internal energy For the sample of n moles, the internal energy:
Internal energy of an ideal gas is a function of gas temperature only

28. Distribution of molecular speeds
Not all the molecules have the same speed
Maxwell’s speed distribution law:
Nvdv – fraction of molecules with speeds in the range from v to v + dv
James Clerk Maxwell
( )

29. Distribution of molecular speeds
Distribution function is normalized to 1:
Average speed:
RMS speed:
Most probable
speed:

30. Thermal expansion
Thermal expansion: increase in size with an increase of a temperature
Linear expansion:
Volume expansion:

31. Thermal expansion

32. Chapter 17
Problem 30
A copper wire is 20 m long on a winter day when the temperature is - 12°C. By how much does its length increase on a 26°C summer day?

33. Questions?

34. Answers to the even-numbered problems
Chapter 16
Problem 22
2500 J/(kg K)

35. Answers to the even-numbered problems
Chapter 16
Problem 40
2.0 × 102 Pa/K

36. Answers to the even-numbered problems
Chapter 17
Problem 18
3.2 × 1023

37. Answers to the even-numbered problems
Chapter 17
Problem 36
11 L