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Temperature and Thermal Energy

Temperature and Thermal Energy. Chapter 12.1. Kinetic Molecular Theory. 1. Everything is made of particles 2. These particles move 3. Hot things move faster than cold things. Definitions. Temperature – a measure of average kinetic energy of an object

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Temperature and Thermal Energy

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  1. Temperature and Thermal Energy Chapter 12.1

  2. Kinetic Molecular Theory 1. Everything is made of particles 2. These particles move 3. Hot things move faster than cold things

  3. Definitions • Temperature – a measure of average kinetic energy of an object • Thermometer - device that measures temperature (and, as a result, average KE)

  4. Heat Flow • Always from hot to cold objects

  5. Heat flow stops only when all objects are in equilibrium (at the same temp)

  6. Example 1 • If A is 75 degrees and B is 25 degrees, at which temperature are they both in equilibrium? • To solve, first add up the different temperatures • Next, divide the total temp by 2 (because we have 2 objects) • This is the equilibrium temperature • Answer = 50 degrees

  7. Absolute zero • The temp at which molecular motion stops • Is this cold or hot??

  8. Temperature conversion • Know how to do these… • 50°C = _______ K • 325 K = ________°C

  9. Temp scales

  10. Conduction • Energy transfer when objects are in direct contact. There must be matter in order for energy to transfer by conduction.

  11. Convection • Energy transfer by air or water currents. • Objects are not in direct contact • Look for currents • Know that hot air and water rises!! • Matter is required for heat transfer by convection

  12. Radiation • Energy transfer thru empty space • No matter is required!! • Its how the sun heats the Earth • Sunbathers are often used as examples of heating by radiation

  13. Examples

  14. Example 2

  15. Example 3

  16. Heat Transfer Formula Q = CmΔT Q = heat gained or lost (J) m = mass in kg C = specific heat (see p.279) ΔT = temp change (K or °C)

  17. Solving for a final temp when 2 objects are mixed or in contact Tf = maCaTai + mbCbTbi maCa + mbCb

  18. Example Problem 1 How much heat is needed to raise the temperature 1.5 kg of water from 22°C to 35°C? m = 1.5 kg ΔT = 15°C C = ?? What is changing temperature? Use the specific heat for whatever is changing temp (see page 279)

  19. Q = 4180 x 1.5 x 15 Q = 94,050 J

  20. Example Problem 2 A 5.0 kg sample of water at 25°C is mixed with 1.5 kg of water at 75°C. What is the final temperature of the mixture? Use the Tf formula…

  21. Tf = 5 x 4180 x 25 + 1.5 x 4180 x 75 5 x 4180 + 1.5 x 4180 Tf = 459800 + 470250 20900 + 6270 Tf = 34°C

  22. Work Page 296 #’s 23 – 24 and 27-28

  23. Phase Change Diagram

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