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Two main goals: Describing energy in a system and how is heat measured.

Two main goals: Describing energy in a system and how is heat measured. Problem with Energy in Education. With your partner, write down your best possible explanation on the whiteboard Use the term energy to describe how a cup of hot coffee cools as it sits on the table.

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Two main goals: Describing energy in a system and how is heat measured.

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  1. Two main goals:Describing energy in a system and how is heat measured.

  2. Problem with Energy in Education With your partner, write down your best possible explanation on the whiteboard • Use the term energy to describe how a cup of hot coffee cools as it sits on the table. • Use the term energy to describe how a 150 g sample of ice at 0.0 ˚C melts and then warms 25.0˚C?

  3. Problem with Energy in Education • “Students cannot use energy to adequately describe or explain everyday phenomena.” With your partner, write down your best possible explanation on the whiteboard • Use the term energy to describe how a cup of hot coffee cools as it sits on the table. • Use the term energy to describe how a 150 g sample of ice at 0.0 ˚C melts and then warms 25.0˚C?

  4. Recall Key Concept 9

  5. Energy Bar Charts Better know as: LOL Diagrams

  6. Energy Bar Charts Better know as: Key Concept 15: Energy bar charts are how we can represent the role of energy when a system is changed.

  7. Constructing an Energy Bar Chart cup coffee Consider this example: A cup of hot coffee cools as it sits on the table. 1. Determine what is in the system Everything else makes up the surroundings

  8. Decide whether Ech is involved In this case, you start with coffee and end with coffee; particles are not rearranged to form new substances So, ignore Ech for now.

  9. Assign values to Eph Key Concept 16: Assign values to Eph- Due to interactions between particles, the energy stored due to the arrangement of particles is ranked: solids < liquids < gases We choose to represent these phases by using: Solids = 1 bar Liquids = 2 bars Gases = 4 bars

  10. Assign values to Eph Key Concept 17: Example LOL for- A cup of hot coffee cools as it sits on the table. Use two Eph bars before and after because starts and ends as a liquid.

  11. Choose bars for Eth depending on temperature Use 4 bars for hot coffee and 2 bars for room temperature coffee Other values might also work; try to be consistent in your representations

  12. Now show energy transfer • The final situation has 2 less bars of E than initial; 2 bars had to leave the system StillKey Concept 17!

  13. Now, consider phase change Key Concept 18: LOL Example- A tray of ice cubes (-8 ˚C) is placed on the counter and becomes water at room temperature • What do we know about the situation? • The system is the tray of ice cubes. • The solid water turns to liquid water - no change in Ech • The Eph increases (solidliquid) • The Eth increases (temp rises) • Now represent these changes in LOL chart.

  14. Initial & Final States • Choice of bars for Eth arbitrary, but consistent. • I generally use 2 bars for room temp and one bar for freezing liquid, -8˚C could be 1 bar.

  15. Account for Energy Energy must flow into system via heating

  16. With Your Partner: • 17. A can of cold soda warms as it is left on the counter. • Extra time do 16.

  17. With Your Partner: • 20. Some water at room temp, is spilled • on the counter and evaporates. • Extra time do 18.

  18. With Your Partner: • 21. Water vapor in the room condenses on a cold surface. • Extra time do 15.

  19. With Your Partner: 19. One of the ice cubes from #18 is placed in a glass of room temperature (25˚C) soda. Do separate bar charts for the ice cube and the soda.

  20. For the Remainder of Class Work on practice problems 3A Complete the rest as homework Answers will be in the purple binder tomorrow Prove It Quiz is not that far way

  21. End Lesson

  22. Two main goals:Describing energy in a system and how is heat measured.

  23. Heat = Temp Mass ×

  24. Day at the Beach

  25. Boiling in a Balloon

  26. Melting Ice

  27. Day at the Beach

  28. White Board Questions A With your shoulder partner, pick one of these demos and write A, B, or C in the corner of your whiteboard. B C

  29. White Board Questions Answer the following questions on your white board. • During your demo did the system gain or lose energy? • Did the objects gain or lose energy at the same rate? Which gained energy at a faster rate? • What do you think accounts for the different rates of energy transfer (or heating)?

  30. White Board Questions Imagine you are given 1g of aluminum and 1g of plastic at room temperature. 4. If you wanted to raise that 1g sample 1°C, which substance would require more energy?

  31. WhiteBoard Questions Imagine you are given 1g of aluminum and 1g of plastic at room temperature. 4. If you wanted to raise that 1g sample 1°C, which substance would require more energy? Heat = Temp Mass What is missing? ×

  32. White Board Questions Imagine you are given 1g of aluminum and 1g of plastic at room temperature. 4. If you wanted to raise that 1g sample 1°C, which substance would require more energy? Heat = Temp Mass Substance specific heating rate × ×

  33. Before You Go… • Discuss with your partner and draw an energy flow diagram for water that evaporates off LeBron James’ sweat band.

  34. End of Lesson

  35. White Board Questions Imagine you are given 1g of aluminum and 1g of plastic at room temperature. 4. If you wanted to raise that 1g sample 1°C, which substance would require more energy? Heat = Temp Mass Substance specific heating rate × ×

  36. SpecificHeat Every Substance has its own specific heating rate: Plastic: 1.131 J/gºC Aluminum: 0.87 J/gºC

  37. Specific Heat Lets break down what plastic specific heat says: Plastic: 1.131 J/gºC Aluminum: 0.87 J/gºC

  38. Specific Heat Write each as a sentence. Plastic: 1.131 J/gºC Aluminum: 0.87 J/gºC

  39. Measuring Heat Heat = Temp. Mass. Substances Specific Heating Rate Or Heat = Temp Mass Specific Heat × × × ×

  40. Specific Heat Demos Water: 4.184 J/gºC Air: 1.02 J/gºC Plastic: 1.131 J/gºC Aluminum: 0.87 J/gºC Water: 4.184 J/gºC Sand: 0.830 J/gºC

  41. Trifold Update

  42. Unit 3 Prove It Quiz • Use practice problems 3A and 3B to study!

  43. End of Lesson

  44. Measuring Heat Heat = Temp. Mass. Substances Specific Heating Rate Or Heat = Temp Mass Specific Heat × × × ×

  45. Specific Heat Key Concept 19: Thespecific heat of any substance is the amount of heat required to raise one gram of that substance one degree Celsius. Some objects require more heat than others to raise their temperature.

  46. Specific Heat: Liquid Water: 4.184 J/gºC Ethanol: 2.46 J/gºC

  47. Specific Heat Capacity What substance, out of everything ever, has the highest specific heat? What substance is the hardest to heat up?

  48. Specific Heat: Water Why is the high specific heat of water important?

  49. Key Concept 20: • At least 80% of the mass of living organisms is water and almost all chemical reactions of life take place in aqueous solution. • Aqueous solution = in water • Thus a high specific heat minimizes fluctuations in temperature inside cells and it also means that sea temperature is quite constant making Earth inhabitable. • Heat Capacity(Start 9:15) The high specific heat of water is important because:

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