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Moving Thermal Energy

1. Moving Thermal Energy. 3. Temperature and Heat. Temperature is the measurement of the avg. KE of the molecules in a material. Heat is the transfer of KE from one material to another. Clip. 4. Heat flows from WARMER to COLDER!. 5. 6. Clip. Conduction.

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Moving Thermal Energy

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  1. 1 Moving Thermal Energy

  2. 3 Temperature and Heat • Temperatureis the measurement of the avg. KE of the molecules in a material. • Heatis the transfer of KE from one material to another. Clip

  3. 4 Heat flows from WARMER to COLDER!

  4. 5

  5. 6 Clip Conduction • The transfer of thermal energy in solids. • Materials must be in direct contact with each other! • Ex: Heating of the bottom of a pot on stove.

  6. 7 • clip Convection • Transfer of thermal energy in liquids and gases. • The matter actuallymovesfrom one place to another.

  7. 8 • Clip Radiation • Transfer of thermal energy by electromagnetic waves(we’ll discuses these more later) • Transferring energy through space...NO MATTER IS REQUIRED!

  8. Exothermic and Endothermic Reactions • A reaction in which heat is given out is exothermic. • A reaction in which heat is taken in is endothermic.

  9. 10 Specific Heat • Adding Energy to a material Causes the • Temperature to go up. • Taking energy away from a substance causes the temp. to • Go down!

  10. Have you ever noticed that on a hot summer day the pool is cooler than the hot cement? • OR maybe that the ocean is cooler than the hot sand? • Why? The sun has been beating down on both of them for the same amount of time........... • It takes more thermal energy to raise the temperature of water that it does the cement! 11

  11. Water absorbs a lot of heat energy before its temperature changes while sand needs little heat energy before its temperature increases. 12

  12. Examples of Specific Heats

  13. 15 Specific Heat • The amount of energy required to raise the temperature of a material (substance). • It takes different amts of energy to make the same temp change in different substances. • We call the amt required: Specific Heat!

  14. 16 Specific Heat of water • The Cp is high because H2O mols. form strong bonds w/each other. • It takes a lot of energy to break the bonds so that the the molecules can then start to move around faster (HEAT UP).

  15. 17 Example:Specific Heat of Water • Cp = 4,184 Joules of energy to raise the temperature of 1kg 1°C. • video clip Why Cp? Cp Stands for “Heat Capacity”

  16. 18 Calculating Specific Heat The Greek letter Δ means “change in”

  17. Sample Calculation for Heat A hot-water bottle contains 750 g of water at 65 °C. If the water cools to body temperature (37 °C), how many calories of heat could be transferred to sore muscles? STEP 1Given: 750 g of water cools from 65 °C to 37 °C SHwater = 1.00 cal/g °C Need: calories of heat transferred STEP 2Calculate the temperature change  T: 65 °C – 37 °C = 28 °C

  18. Sample Calculation for Heat STEP 3Write the heat equation: Heat (cal) = mass(g) x  T x SH STEP 4Substitute given values and solve for heat: 750 g x 28 °C x 1.00 cal g °C = 21 000 cal

  19. Learning Check How many kilojoules are needed to raise the temperature of 325 g of water from 15.0 °C to 77.0 °C? 1) 20.2 kJ 2) 84.3 kJ 3) 105 kJ

  20. Solution 2) 84.3 kJ STEP 1Given: 325 g of water warms from 15.0 °C to 77.0 °C SHwater = 4.184 J/g °C 1 kJ = 1000 J Need:kilojoules of heat needed STEP 2 Calculate the temperature change  T: 77.0 °C – 15.0 °C = 62.0 °C STEP 3Write the heat equation: Heat (joules) = mass (g) x  T x SH

  21. Solution (continued) STEP 4Substitute given values and solve for heat: 325 g x 62.0 °C x 4.184 J x 1 kJ g °C 1000 J = 84.3 kJ (2)

  22. A copper ornament has a mass of 0.0693 kg and changes from a temperature of 20.0°C to 27.4ºC. How much heat energy did it gain? A200 J C540 J B460 J D740 J 24

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