Chapter 6, Thermal Energy and Heat

Chapter 6 Thermal Energy and Heat (complete the outline)   Part 1: 6.1 Temperature and Thermal Energy (complete the outline) Temperature A measure of the average kinetic energy of the individual particles in an object. In hot objects, its particles are moving faster, so they have greater Kinetic energy In cold objects, its particles are moving slower, so they have less Kinetic energy Temperature Scales – There are 3 temperature scales . Fahrenheit Scale – In the US, this is the most common scale Water freezes at 32 F. Water boils at 212 F.

Celsius Scale (like Centigrade scale) – most used in the world. water boils at 100 C. water freezes at 0 C. Kelvin Scale – SI unit for Temperature. Units are the same size compared to the Celsius Scale. K = add 273 (insert formula to convert C to K) C = subtract 273 ( insert formula to convert K to C) Water boils at 373 K Water Freezes at 273 K Based on Absolute Zero - (define ab. zero) The lowest temperature possible Temp for absolute zero is -273 C or 0 K Thermal Energy Thermal energy is the total energy of all of the particles in a substance.

3 Ways to Transfer Heat, pgs 171 – 174 1) What is heat? 2) What are the 3 ways that heat can transfer? 3) Explain conduction, include examples. 4) Explain convection, include examples. 5) What is a convection current? 6) Explain radiation, include examples. 7) In what direction does heat move? *

Heat Heat is the movement of thermal energy from warm substances to cool substances. It only moves 1 way: from hot to cold. Eg. Ice into warm soda – ice doesn’t make soda cold; soda makes ice warm. No such thing as cold: it’s lack of heat 3 ways for heat to transfer: conduction, convection, and radiation *

Conduction Way heat transfers in solids. Heat transfers from 1 molecule of matter to the next, without the movement of matter. Eg. A frying pan on an electric stove *

Convection Transfers heat is a fluid (liquid or gas) Heat is transferred by the movements of currents in a fluid. A convection current: a circular flow of motion. Hot fluid rises and cold fluids sink. Eg: boiling water or air in a heated room *

Radiation Transfer of energy by electromagnetic waves. No matter is needed for this transfer of heat. Eg: heat from sun or feeling the heat of a bonfire or heat lamp. *

Conductors vs. Insulators conduct heat well feel cool to touch examples are: metal, glass, water Demo: arm on wood and metal Insulators do not conduct heat well feel warm to touch examples: wood, wool, paper, air, cloth, feathers *

Specific Heat Specific Heat - the amount of energy required to raise the temperature of a 1 kilogram sample by 1 Kelvin. It’s a property of matter (just like density or boiling point). The unit for it is Joules per kilogram-kelvin specific heat of water, 4180 J/kg.K : absorbs a lot of heat before its temperature increases. makes a good coolant. *

Specific Heat, Continued specific heat of copper, 385 J/kg.K heats up quickly so makes good pots and pans. see page 176 for table of specific heats Calculation: Heat gained=mass X specific heat X change in temp Q = m C ΔT *

Sample Calculation How much heat is required to raise the temperature of 6 kilograms of water by 3 kelvin degrees? Q = m C ΔT = 6 kg X 4180 X 3 K = 75240 J Do page 177 Number 4 *

6.3 Thermal Energy and States of Matter A) 3 common states of matter 1. Solid – particles close together in fixed position. Can’t change its shape or volume. 2. Liquid – Particles are close but they aren’t as packed as a solid. Can change its shape but not its volume 3. Gas – particles are far apart and moving fast. Can change its shape and volume. *

B) Changes of State – a physical change B) Changes of State – a physical change. When you add or remove thermal energy one state of matter changes into another. C) Solid – Liquid Changes of State – melting and freezing (occurs at melting point temp (same as freezing point temp) 1) Melting: Solid to liquid, when you add thermal energy 2) Freezing: Liquid to solid, when you remove thermal energy, *

D) Liquid-Gas Changes of State - vaporization and condensation 1) Vaporization – liquid to gas by adding thermal energy. 2 ways: Evaporation – occurs on surface of liquid, at normal temps e.g.: hang a wet shirt out to dry Boiling – occurs all through liquid at the boiling point 2) Condensation – gas to liquid by removing thermal energy. E.g: dew *

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E) Thermal Expansion: as thermal energy increases, particles in matter spread out and the substance expands. If you cool it, it contracts (Exception IS WATER!) 1. Thermometers – hollow tube filled with alcohol or mercury, it expands as things get hotter. 2. Expanding Teeth – fillings are cool on the dentists tray, gain heat in your mouth and expand to fill the drilled whole in your tooth. 3. Thermostats – used to turn heaters on and off. Uses a “Bimetallic strip” *

6-4 uses of heat, pgs 187 - 190 1. What are heat engines? 2. What is combustion? 3. Explain the difference between an internal combustion engine and an external combustion engine. 4. Give examples of each type of engine. 5. Use page 189 and describe each step in a four-stroke engine. 6. Explain how a refrigerator works. *

Four Stroke Engine The Otto cycle is characterized by four strokes, or straight movements alternately, back and forth, of a pistona piston inside a cylinder: intake (induction) stroke compression stroke power (combustion) stroke exhaust stroke *