1. Temperature, Heat, and the First Law of Thermodynamics
Chapter 18
Temperature, Heat, and the First Law of Thermodynamics

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

9. Chapter 18
Problem 19

10. 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):

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

12. Chapter 18
Problem 37

13. Heat and work
Thermodynamic cycle

14. The first law of thermodynamics
Work and heat are path-dependent quantities
Quantity Q – W = Eint (internal energy) is path-independent
1st law of thermodynamics: the internal energy of a system increases if heat is added to the system and decreases if work is done by the system

15. The first law of thermodynamics
Adiabatic process: no heat transfer between the system and the environment
Isochoric (constant volume) process
Free expansion:
Cyclical process:

16. Chapter 18
Problem 48

17. Heat transfer mechanisms
Thermal conduction
Conduction rate:
Thermal resistance:
Conduction through a composite slab:
Thermal conductivity

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

19. Chapter 18
Problem 52

20. Heat transfer mechanisms
Convection

21. Heat transfer mechanisms

22. Answers to the even-numbered problems
Chapter 18:
Problem 4
320º F;
(b) -12.3º F

23. Answers to the even-numbered problems
Chapter 18:
Problem 10
1.1 cm

24. Answers to the even-numbered problems
Chapter 18:
Problem 22
109 g

25. Answers to the even-numbered problems
Chapter 18:
Problem 44
− 200 J;
(b) − 293 J;
(c) − 93 J

26. Answers to the even-numbered problems
Chapter 18:
Problem 50
0.42 m;
(b) 7.4 km