Chapter 10

1. Chapter 10 Heat Transfer and Change of Phase

2. 10.1 Conduction • If you hold fireplace poker at unheated end, it will soon become too hot to hold. • Conduction- electrons (especially those of metals) migrate towards colder ends • Electrons collide • Metals have very loose electrons, so easy to travel (also best to conduct electricity) • Silver, copper, aluminum, iron are good conductors • Wool, wood, paper, cork, plastic foam = poor conductors

3. Insulators • Poor conductors are insulators- electrons are firmly attached • Wood is an insulator- why have wooden spoons for stirring hot pasta or why walk on hot coals and not get burnt • Air is an insulator- hand in hot oven air okay, not so with metal in oven! • Snow is an insulator- ground is warm in winter, and animals use snow blankets • Insulation in house does not prevent transfer of heat, just delays loss

4. 10.2 Convection • Convection- transfer of heat by motion of fluid • Used by gas and liquid (currents) • Fluid heated from below, molecules at bottom move faster, spread apart, are less dense, and move upward while denser, colder molecules move to bottom and then are heated. • Self-stirring (wind) • Cooling by expansion- opposite from compression

5. 10.3 Radiation • Radiation (not radioactivity)- how sun transfers heat in forms of electromagnetic waves • Waves- radio through infrared • Short waves- can’t see, quick • Long waves- travel far, slow (Chapter 12-14) • See wavelength and frequency pictures and examples on board, as well as cool, medium, and hot waves

6. Radiation • f ~ T (frequency ~ temperature) • Frequency lower than visible • Earth is relatively cool, but Earth gives off terrestrial radiation • Sun and Earth glow (cores radiate) • You emit radiation • Other warm things that give off light • Greenhouse effect • Dark object absorb energy and emits a lot of energy (dark vs. light mug)

7. Reflection • Energy can be reflected- bounced off • Some absorption always occurs • Your pupil is black because it absorbs light without reflection (unless get red-eye in photographs) • Light-colored buildings cooler in summer- reflect radiant energy but don’t give away much energy in winter

8. 10.4 Matter Changes Phase • States of matter • Solid • Liquid • Gas • Plasma (fluorescent lamps) • These are in order of slowest to fastest

9. 10.5 Evaporation • Liquid to gas • At surface, gain speed, fly away when gain more energy than others • Why sweat- so sweat will evaporate and cool us (animals do not sweat, so they pant or roll in cool mud) • Solid to gas- sublimation, where there is a lot of energy (dry ice)

10. 10.6 Condensation • Condensation- opposite of evaporation • Gas-> liquid • Gas attracted to liquid, slows, gets stuck • Why cold after shower, condensation stopped, evaporation starting • Colder in dry areas (Phoenix)

11. 10.7 Boiling • Boiling- evaporation of liquid beneath surface • Bubbles rise to surface • Water boils at 95 degrees in higher elevations, lower pressure • See drawing on board of vacuum • Boiling, like evaporation, cools (otherwise, temperature keeps rising)

12. 10.8 Melting and Freezing • Melting- solid-> liquid • Freezing- liquid-> solid

13. 10.9 Energy needed to Change • Energy needed to change states of matter • Heat of fusion (335 J/g) • Heat of vaporization (2255 J/g) • See phase diagrams on board • Example calculations of states of matter