1. CHAPTER 9 THERMODYNAMICS
UNIT 2 MECHANICS
CHAPTER 9
THERMODYNAMICS

2. CHAPTER 9A – THERMAL ENERGY
Objectives:
Summarize the development of the theory of thermal energy
Describe how Count Rumford disproved the caloric theory
Explain temperature change in terms of the kinetic-molecular theory
Compare and contrast thermal and internal energy
Assignment: Section Review, page 205

3. Early Theories of Heat Many more scientists!
Greek philosophers - Heraclitus, Socrates, Plato
Francis Bacon, Daniel Bernoulli, Lavoisier, Sadi Carnot, Benjamin Thompson, Robert Mayer, James Prescott Joule, William Thomson
Let’s Read page 200, section 9.1 & 9.2
Caloric theory
An obsolete model of heat that considered heat a material fluid that flowed from hot to cold objects

4. Kinetic-Molecular Theory of Heat
The caloric theory was unable to explain all observations
A new model was needed…
Remember the kinetic-molecular theory?
Let’s Read page 201, section 9.3
Facet – Nicolas Sadi Carnot

5. Nature of Thermal Energy
Atoms, molecules, ions and their subatomic particles are in constant motion and have kinetic energy
They exert attractive or repulsive forces that generate potential energies
The sum of all these energies is called the internal energy of matter and cannot be measure!
Thermal energy
The sum of all the kinetic energies of its particles
Part of internal energy, but not the same
Can not be measured directly, but changes can
Heating or cooling
The transfer of particle kinetic energy

6. How Can we use Thermal Energy?
Stirling engine
A piston engine containing a working gas that is transferred between hot and cold heat exchangers to move the pistons
The heat source comes from outside the engine
Converts thermal energy to mechanical energy at near maximum theoretical efficiency

7. CHAPTER 9B - TEMPERATURE
Objectives:
Give examples of thermometric properties
Compare and contrast the Fahrenheit, Celsius, and absolute temperature scales
Explain how a fiducial point is chosen for a temperature scale
Convert temperatures between all three temperature scales
Describe how a thermometer works
Assignment: Section Review, page 210

8. Thermometric Properties
Who determines whether you are hot or cold?
Those terms are subjective, scientists need something objective to measure temperatures
Temperature
A measure of the average kinetic energy of the particles in a substance
The hotness or coldness of an object, measure in degrees
Change depends on temperature scale
Thermometer
An instrument that uses a thermometric property to measure and display temperature

9. Temperature Scales
Scientists needed a way to make sure that the whole world was using the same scale to record temperature
Fiducial point
Fixed, precise, and easily reproducible values in a dimension used to calibrate a measuring scale
Examples: boiling and melting points

10. Temperature Scales Fahrenheit scale
A temperature scale with fiducial points at the freezing point (32) and boiling point (212) of pure water at 1 atm of pressure
Mercury verses alcohol based?
180o difference between melting and boiling point
Daniel Gabriel Fahrenheit

11. Temperature Scales Celsius scale
A temperature scale with fiducial points at the freezing point (0) and the boiling point (100) of pure water at 1 atm pressure
100o difference between melting and boiling point
Anders Celsius
Decimal scale
Most of the world uses this scale, not the US
Two formulas for conversions:
Tc= 5/9(Tf+40)-40
Tf=9/5(Tc+40)-40
Why 5/9 and 9/5?
What is bigger 1 degree Celsius or 1 degree Fahrenheit?

12. Temperature Scales Kelvin scale Easy formulas for conversion:
The absolute temperature scale, whose theoretical zero point is absolute zero
No degree signs
Single fiducial point is the triple point of pure water (273.16)
The pressure and temperature conditions at which the solid, liquid, and gaseous phases of a substance simultaneously exist in a stable condition
One Kelvin is the same size as one degree Celsius
Easy formulas for conversion:
Tk=Tc
Tc=Tk

13. Matter and Temperature
Temperature can have significant effects on important properties of matter
1. Thermal expansion
A thermal property of most materials in which length or volume increase in proportion with increasing temperature
2. Electrical resistance
Ability to conduct electricity
3. Viscosity
A fluid’s resistance to flow

14. CHAPTER 9C - HEAT Objectives: Assignment: Section Review, page
Compare and contrast heat and thermal energy
Describe the flow of thermal energy
Describe the three methods of heat transfer and give an example of each
Summarize the physical properties of insulators and conductors
Describe how thermal energy affects matter’s volume and ability to allow electricity to pass through it
Compare and contrast heat capacity and specific heat
Do calculations with the specific heat and heat capacity formulas
Explain the changes in thermal energy and temperature for an object that is heated from its solid state to its gaseous state
Assignment: Section Review, page

15. Facet page 211 Second Law of Thermodynamics Entropy
Law stating that every natural process proceeds toward a condition of lowest usable energy and highest entropy
Entropy
The measure of a system’s randomness of disorder
Greater entropy = greater disorder

16. Heat Transfer Heat Occurs through one of three processes
A quantity of thermal energy that flows from one system to another
Occurs through one of three processes
Conduction
Convection
Radiation

17. Conduction
The flow of thermal energy from a hotter to a cooler object by direct contact
The flow of an electrical current through a conductor
A material through which heat and electricity easily flow
Usually materials that contain mobile electrons, such as most metals
Wants to reach a thermal equilibrium
The condition of a system that is at the same temperature as its surroundings so there is no net flow of thermal energy
Chief process by which thermal energy moves through solids

18. Convection
The transfer of thermal energy from one location to another through the movement of matter
Thermal energy transfer between fluids
Natural convection
Occurs under the influence of gravity
Convection current
A flow of matter in a fluid as warmer, lower density fluid is displaced upward by cooler, denser fluid flowing downward
Cyclical path
Only occurs in a gravitation field
Forced convection
Atmospheric convection

19. Radiation
Nuclear particles or electromagnetic waves that radiate away from their sources
A method of heat transfer through radiant (electromagnetic) energy
What should you wear on a hot day, a black shirt or a white one?

20. Insulation & Thermal Resistance
Insulators
A material that does not easily conduct thermal energy or electricity
Poor conductors with tightly bound valence electrons
What is the particle difference between conductors and insulators?
Aerogels
The best artificial insulators
Facet page 215

21. Heat Capacity
Every object has a particular relationship between the amount of thermal energy absorbed and the temperature change experienced
Heat capacity
The amount of thermal energy an entire object must gain or lose to change its temperature 1oC
Depends on the mass and thermal properties of the substance(s) in the object
Formula:
C=Q/ t
C=heat capacity Q=thermal energy T=temperature in Celsius

22. Specific Heat Capacity
The amount of thermal energy 1g of a substance must gain or lose to change its temperature 1oC
Calorimeter
A device that measure thermal energy transfer between objects contained in a chamber insulated from its surroundings
Formula:
Q=mcspt
Example Problem 9-1

24. Heat and Phase Changes Latent heat of fusion (Lf)
The amount of thermal energy absorbed per gram as a solid melts (fuses) at its melting point
The same amount of heat per gram must be released to freeze the substance
Formula: Q=mLf
Latent heat of vaporization (Lv)
The amount of thermal energy absorbed per gram as a liquid vaporizes
The same amount of heat per gram must be release to condense the vapor to a liquid
Formula: Q=mLv

25. TOMORROW!! Vocabulary Quiz Complete Chapter Review in Class
Includes all vocabulary throughout the entire chapter, PowerPoints, and board; not just the box at the end.
Complete Chapter Review in Class
Study for Chapter 9 Test