Chapter 14: Thermal Energy & Heat 4/22/2017

Introduction Heat is the transfer of thermal energy. 4/22/2017

Topics of Discussion Temperature , Thermal Energy, and Heat (Section1) The Transfer of Heat (Section 2) Thermal Energy and States of Matter (section 3) Uses of Heat (Section 4) 4/22/2017

TEMPERATURE and THERMAL ENERGY (Section one) Temperature is the measure of the average kinetic energy of the individual particles in matter. Three common Temperature scales for measuring temperature Fahrenheit Celcius Kelvin 4/22/2017

Fahrenheit (Section one) U.S. System Water Freezes at 32o Water Boils at 212o 180 equal intervals between freezing and boiling called degrees Fahrenheit (oF) Absolute zero is -460o 4/22/2017

Absolute Zero (Section one) Absolute zero is the lowest temperature possible. At this temperature, no more energy can be removed from matter. -460oF -273oC 0 K 4/22/2017

Celcius Scale (Section one) This system is used in most of the world. Water Freezes at 0o Water Boils at 100o 100 equal intervals between freezing and boiling called degrees Celcius (oC) Absolute zero is -273o 4/22/2017

Kelvin Scale (Section one) This system is used most in physical science. Units on the Kelvin scale are the same size as those in Celcius – called kelvins (K) Water Freezes at 273o Water Boils at 373o Absolute zero is 0o The Kelvin scale is defined so that zero is absolute zero. 4/22/2017

Thermal Energy (Section one) Thermal energy is the total energy of all of the particles. Heat is thermal energy moving from a warmer object to a cooler object. (Only = One way.) 4/22/2017

Thermal Energy (Section one) Specific Heat – The amount of energy required to raise the temperature of one kilogram of a substance by 1 kelvin. Δ energy = Mass X Specific heat X Δ temperature (Δ = change) 4/22/2017

Thermal Energy (Section one) Units = Joules per kilogram-Kelvin J/(kg·K) 4/22/2017

The Transfer of Heat (Section 2) Heat is transferred by: Conduction, Convection, and Radiation. 4/22/2017

Conduction (Section 2) Heat is transferred from one particle of matter to another without the movement of matter itself. Ex: A metal spoon in a pot of water on an electric stove. The fast moving (hot) particles of the element collide with the slow (cold) particles of the pot and energy is transferred. 4/22/2017

Convection (Section 2) Heat is transferred by the movement of currents within a fluid (liquid or gas.) Ex: Water heating in a pot on the stove. Differing densities cause the water to flow in a circular motion known as a convection current. 4/22/2017

Radiation (Section 2) The transfer of energy by electromagnetic radiation. Radiation does not require matter to transfer thermal energy. Ex: Heat from a fireplace, the sun, heat lamp, and a microwave oven. 4/22/2017

Heat Moves One Way (Section 2) If two objects have different temperatures , heat will flow from the warmer object to the colder one. 4/22/2017

Conductors and Insulators (Section 2) Conductor – A material that conducts (transfers) heat well. Ex: metal. Insulator – A material that does not conduct heat well. Ex: Wood, Glass and gasses. 4/22/2017

Thermal Energy and States of Matter (Section 3) Most matter on Earth can exist in three states: Solids Liquids Gases 4/22/2017

Solids (Section 3) Ex: Ice cube & text book Tightly packed particles Particles in fixed position (vibrate) Definite volume & shape 4/22/2017

Liquids (Section 3) Ex: Water & Molten steel Particles close together (further than solid) Particles can move around Definite volume, random shape 4/22/2017

Gases (Section 3) Ex: Steam & air Fast moving / far apart particles Particles free to move Random volume, random shape (Expand to fit space available) 4/22/2017

Changes of State (Section 3) Change of state is the physical change from one state of matter to another. Matter will change from one state to another if thermal energy is absorbed or released. Solid-Liquid Liquid-Gas (Temperature = constant) 4/22/2017

Solid – Liquid Changes of State (Section 3) Melting From solid to liquid A solid absorbs thermal energy Melting point = temperature at which a solid changes to liquid Freezing From liquid to solid Matter releases thermal energy Freezing point = temperature at which a liquid changes to solid 4/22/2017

Liquid - Gas Changes of State (Section 3) Vaporization From liquid to gas Liquid absorbs thermal energy Evaporation = vaporization on surface Boiling = vaporization within liquid Boiling point = temperature at which a liquid changes to gas Condensation From gas to liquid Thermal energy decreases 4/22/2017

Thermal Expansion (Section 3) As thermal energy of a substance increases, its particles spread out and the substance expands. Thermometers Expanding liquid – Mercury or alcohol Thermostats Expanding bimetallic strips 4/22/2017

Uses of Heat (Section 4) Heat Engines – External Combustion Engines Transform thermal energy to mechanical energy External Combustion Engines Fuel is burned outside the engine howstuffworks.com/steamengine Internal Combustion Engines Fuel is burned in cylinders inside the engine. http://auto.howstuffworks.com/4Stroke 4/22/2017

Internal Combustion Engines (Section 4) Gasoline and Diesel Pistons move up and down (one stroke) to drive crankshaft Two Stroke Four- Stroke Intake Stroke Compression Stroke Ignition Power Stroke, and Exhaust Stroke 4/22/2017

Refrigerators (Section 4) A refrigerator is a device that uses an outside energy source to transfer thermal energy from a cool area to a warm area. Refrigerant – The substance that absorbs and releases heat in a refrigerator http://home.howstuffworks.com/refrigerator 4/22/2017

Key Terms Absolute Zero Heat Conduction Convection Convection Current Radiation Insulator/Conductor Specific Heat State Change of State Melting (point) Freezing (point) Boiling (point) Condensation Thermal Expansion Heat Engine Internal Combustion External Combustion 4/22/2017