CHAPTER 9 THERMODYNAMICS UNIT 2 MECHANICS CHAPTER 9 THERMODYNAMICS

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

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

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

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

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

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

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

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

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

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?

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+273.15 Tc=Tk-273.15

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

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

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

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

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

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

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?

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

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

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

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

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