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Energy

Energy. Unit 6. What is Energy?. A burning match releases energy. Source: ElektraVision/ PictureQuest. A Hindu firewalking ceremony in the Figi Islands. Could you do this?. Source: Jack Fields/Photo Researchers, Inc. Energy. Capacity to do work or produce heat

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Energy

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  1. Energy Unit 6

  2. What is Energy?

  3. A burning match releases energy. Source: ElektraVision/ PictureQuest

  4. A Hindu firewalking ceremony in the Figi Islands. Could you do this? Source:Jack Fields/Photo Researchers, Inc.

  5. Energy Capacity to do work or produce heat Capacity to move or change matter Energy Notes

  6. Work Examples Moving an object over a distance against a resisting force Energy stored in the organized motion of molecules A car traveling down the street A train moving down the tracks Pushing a book across the desk Energy Notes

  7. Stored Energy of position (water wheel, book on desk) Chemical energy (gas, food, batteries) Motion Mechanical energy (moving parts of machines) Thermal energy (Sun’s heat) -Light Vibration of molecules Potential Kinetic Radiant Sound Types of Energy

  8. Law of Conservation of Energy In any chemical or physical process, energy is neither created nor destroyed. Different forms of energy are equivalent. A particular amount of one type of energy can be converted into an exactly amount of another type of energy. Energy Notes

  9. Energy Measurement Joule

  10. Unit: Conversion (c to J) Metric = joule (J) US = calorie (c) 1 calorie is the amount of heat needed to raise 1 g of H2O by 1 °C 1000cal = 1Cal = 1 kilocalorie = food Calories 4.184 J = 1 cal Energy Notes

  11. Example A student uses 30 J of energy putting books on the shelf in the classroom. How many calories of energy did the student exert? A student eats an entire bag of plan popcorn which contains 60.1 Calories. How many Joules of energy is this? STOP Period 6 Energy Notes

  12. Brain Teaser • Explain why the rug on your floor feels warmer than the tile in the same room • Convert 200 Calories to Joules • 4.184 Joules = I calorie • 1 Calorie = 1000 calories

  13. Agenda • Brain Teaser • Collect Energy Lab Packet • Energy Notes: • Heat and Temperature • Specific Heat • Homework • Temperature Conversion Worksheet

  14. Heat and Temperature Continue on this slide (P5)

  15. Figure 3.12: Equal masses of hot water and cold water separated by a thin metal wall in an insulated box. Is anything going to happen?

  16. Figure 3.13: The H2O molecules in hot water have much greater random motions than the H2O molecules in cold water.

  17. Figure 3.14: The water samples now have the same temperature (50°C) and have the same random motions.

  18. Heat Examples Energy transferred from one body to another due to a temperature difference. Energy stored in the random motion of molecules Sunlight heating the earth Hot plate with beaker of water Heat and Temperature

  19. Exothermic Endothermic System that releases energy into its surroundings Release energy because a change has occurred Combustion reactions System that takes energy in as heat from the surroundings Need energy from outside source in order for a change to occur Phase change – boil water Heat and Temperature

  20. Endo vs. Exo • Why are these types of reactions useful? • What are some examples in your daily life?

  21. Temperature 3 scales Measure of the average kinetic energy of the particles in a sample of matter. Fahrenheit (ºF) Celsius (ºC) Kelvin (K) Temperature

  22. Converting between ºC and K Example Practice ºC = K – 273 K = ºC + 273 Normal human body temperature is 37 ºC. What is your temperature in K? Surgical instruments must be sterilized at 170 ºC. What is this in K? Temperature

  23. Converting between ºC and ºF Example Practice ºC = 5/9(ºF – 32) ºF = 9/5 ºC + 32 It is 100 ºF outside. What temperature is this in ºC? The boiling point of methanol is -164 ºC. What is the boiling point is ºF? Temperature

  24. Heat versus Temperature(continue on this slide P2,4) • Heat • Energy that transfers from one object to another because of a temperature difference between them. • Temperature • A measure of the average kinetic energy of the particles in a sample of matter

  25. Refer to Temperature Worksheet

  26. Brain Teaser (1/17) • Convert 200 Calories to Joules

  27. Agenda • Brain Teaser • Notes: Specific Heat and Calorimetry • Post Lab Activity: Energy Lab • Homework • Practice Problems 1-6

  28. Specific Heat and Calorimetry

  29. Specific Heat What this means amount of heat that can be absorbed by 1 gram of material when its temperature increases by 1oC; unit = J/g oC What bench would you rather sit on, wood or iron, in the summer in AZ? Why? Specific Heat and Calorimetry

  30. Specific Heat • Which holds more heat when exposed to 120oF sunlight -- a wood or an iron bench (both at the same temperature)? • Compare the specific heat capacities. Iron 0.448 J/goC, wood 1.76 J/goC • The wood bench holds onto more heat so it does not transfer as much to you.

  31. Calorimetry Calorimeter Measurement of the amount of energy released or absorbed during a chemical reaction Device used to measure the transfer of energy to water Specific Heat and Calorimetry

  32. Complex Calorimeter

  33. Test Tube Thermometer Stirring Rod Water Sealed Container Reaction Simple Calorimeter

  34. Endothermic- reaction absorbs energy temperature of the surrounding water goes down Exothermic - reaction gives off energy temperature of the surrounding water goes up Endo vs. Exo Energy

  35. How does the Heat Flow and How do you Know?

  36. Q= mCpT Mass of the water in the calorimeter (units = grams) Specific Heat of water 3. Change in the water’s temperature. T = Tfinal- Tinitial (units = ºC) Three factors determine the amount of energy (Q) transferred to or from the water.

  37. Example 1 Practice 1 How many calories must be added to 5000 g of water to change it temperature from 20 to 30ºC? How many calories are needed to increase the temperature of 150.0 grams of water from 40.0 to 65.0ºC? specific heat for water Q= mCpT

  38. Example 2 Practice 2 A 2.0 x104 grams sample of water has its temperature raised by 3ºC. How many Joules of energy was produced? What is the number of Joules needed to increase the temperature of 50.0 grams of water 15.0ºC? specific heat for water Q= mCpT

  39. Example 3 Practice 3 If 500.0 g of water at 25ºC loses 2500 calories, what will be the final temperature? What is the final temperature after 80.0 calories is absorbed by 10.0 grams of water at 25ºC? specific heat for water Q= mCpT

  40. Example 4 Practice 4 What temperature change,in Celsius, is produced when 6.0 x102 grams of water gives off 9.60 kilocalories? What is the change in temperature when 640 calories is given off by 40 grams of water? specific heat for water Q= mCpT

  41. Example 5 Practice 5 What is the specific heat of lead if a 30.0 g piece of lead undergoes a 250ºC change while absorbing 229.5 calories? What is the specific heat of an unknown substance if the addition of 950 J of heat energy caused a 20 gram sample to warm from 18ºC to 42ºC? Q= mCpT

  42. Example 6 Practice 6 A quantity of water is heated from 25.0ºC to 36.4ºC by absorbing 325 calories. What is the mass of the water? What is the mass of a piece of copper that undergoes a 25.0ºC temperature change when it absorbs 755 J of energy? Copper has a specific of Q= mCpT

  43. PreLab: Energy Content in Foods Time to get your lab books ready for Lab! Use the lab handout to help you complete all of the following according to the grading rubric. • Title • Purpose • Background information • Materials • Procedure and safety • Set up data table

  44. Class Results

  45. Class Results 6th Period

  46. Review Lab- Energy Content in Foods • Food energy is expressed in Calories. 4.184 kJ in 1.000 Calories. Based on the class average for peanuts, calculate the number of calories in a 50.0 g package. • Product labels. Determine a serving size and use the class average to calculate the number of calories present in a single serving. Compare your results to the nutritional information.

  47. Review Lab- Energy Content in Foods • What are 2 possible sources of error? What could be done to reduce these errors? • How does calorimetry make use of the law of conservation of energy? • What generalization can you make about the relative energy content of fats and carbohydrates?

  48. Product Labels 16 oz = 453.59 g Peanuts – 1 oz, 180 Calories Cashews – 1 oz, 160 Calories Popcorn – 1 cup popped, 25 Calories (7g~1 cup) Marshmallow – 30 g, 100 Calories

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