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Ch. 9 Heat

Ch. 9 Heat. Notes, Day 1. OBJECTIVES FOR THE UNIT: 1a. Be able to draw and describe the Paradigmatic Thermal Process. Explain how this process shows thermal equilibrium. 1b. Describe how the Paradigmatic Thermal Process relates to Heat

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Ch. 9 Heat

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  1. Ch. 9 Heat

  2. Notes, Day 1

  3. OBJECTIVES FOR THE UNIT: • 1a. Be able to draw and describe the Paradigmatic Thermal Process. Explain how this process shows thermal equilibrium. • 1b. Describe how the Paradigmatic Thermal Process relates to Heat • 2. Define temperature within the contexts of thermal equilibrium and a thermoscope. • 3. Predict how temperature will change as the KE of particles changes. • 4. Be able to convert between Celsius and Kelvin. • 5a. Describe what happens to particles and gases at 0 K. • 5b. By graphing P vs. T (as degrees Celsius), predict that where gases have 0 pressure = 0 K (-273 C) • 6a. Describe the relationship between internal energy (U), mass (m), specific heat (c), and temperature (T) • 6b. Lab Place water, water with salt in it, and ice on the same burner. Observe which boils faster. Predict how much more energy was needed to heat the regular water than the ice water. Describe the relationship between energy/ ∆T that leads to c. [ The ice situation will be discussed later in the unit ] • 7. Be able to solve word problems involving relationships defined in this unit. • 8. Use the concept of Calorimetry to determine the specific heat capacity of an unknown in a lab situation. • 9. Describe some of the factors that can lead to a large or small Latent Heat

  4. OBJECTIVES FOR DAY 1: • 1a. Be able to draw and describe the Paradigmatic Thermal Process. Explain how this process shows thermal equilibrium. • 1b. Describe how the Paradigmatic Thermal Process relates to Heat • 2. Define temperature within the contexts of thermal equilibrium and a thermoscope. • 3. Predict how temperature will change as the KE of particles changes. • 4. Be able to convert between Celsius and Kelvin.

  5. Heat PreTest • 1. Define Heat • 2. Use a picture to describe how heat could be measured. • 3. Use a picture to show what would happen (energetically) if a hot metal block is placed in a gallon jug of room temperature water. • 4. You have two gases in identical containers. The same type of gas and number of gas molecules are in both containers. Container 1 has a gas pressure that is 5 times greater than Container 2. Describe on the atomic level what will happen to the gas molecules if these two containers are combined. • 5. Your friend tells you that when two objects are in thermal equilibrium, it means that no heat will flow between the two objects. Support or critique his opinion. • 6. Draw a graph to show all the energetic changes that will happen to an ice cube as heat is applied steadily to the ice cube until it all becomes a gas.

  6. Demonstration Glass of hot water, set it out, what will happen? • What happens to the temp. of each? • How is energy transferred? • What do things look like at a molecular scale? • Is the process reversible AT ALL? • What does the situation look like at equilibrium? Is it STATIC?

  7. The Paradigmatic Thermal Process

  8. How does HEAT relate to the paradigmatic thermal process? • Heat is the energy transferred from one object to another because of a difference in temperature between the two. • Heat energy travels from hot things to cold things.

  9. In the Paradigmatic thermal process, heat energy is transferred IRREVERSIBLY from the thing at a higher temperature to the object at a lower temperature. • This means that the reverse interaction will NOT occur at all. • We will tie this idea to the idea of probability in the next unit on thermodynamics.

  10. Thermoscope: A device that measures temperature. • T = 273.15 K * (P/Pt.p. of water)

  11. What happens if two things are in thermal equilibrium? (soccer ball/air)

  12. What happens if two objects are in thermal equilibrium? • A thermoscope will measure the same temperature for each. • Heat (J) will flow equally between the two objects.

  13. What do heat and temperature mean on an atomic scale?

  14. Temperature is proportional to the kinetic energy of atoms and molecules. • What happens as we add energy to a system of atoms?

  15. Put these two in close contact, what will happen?

  16. Internal energy (U) = the energy of a substance due to its motion. Increases as temperature is increased.

  17. Temperature readings are only valuable if they are stable.

  18. What will happen? • Matter expands as its temperature increases. • Temperature increases as energy is given.

  19. What will happen to the pressure? • Increases

  20. Thermal expansion. • Coefficient of Volume Expansion Gases have the largest value. They increase in volume the most when temp. increases.

  21. Fahrenheit to Celsius Tf = 9/5C + 32 • K = C + 273.15

  22. End of notes, day 1

  23. Notes, Day 2

  24. Objectives For DAY 2: • 6. Describe what happens to particles and gases at 0 K. • 7. By graphing P vs. T (as degrees Celsius), predict that where gases have 0 pressure = 0 K (-273 C) • 8. Describe the relationship between internal energy (U), mass (m), specific heat (c), and temperature (T) • 10. Be able to solve word problems involving relationships defined in this unit.

  25. 0 Kelvin is called Absolute 0. • At this temperature, particles stop moving, and gases have a pressure of 0.

  26. What will happen at absolute 0?

  27. We will do a graphing activity regarding absolute 0 later in the week.

  28. Conservation of Energy: • deltaPE + deltaKE + deltaU = 0

  29. Specific Heat Capacity c the energy needed to change the temperature of 1 kg of a substance by 1 K.

  30. dU = mcdT • We will assume no work is done, so Q = U.

  31. All substances have a unique c value. • Water has a very high c, because hydrogen bonds make water stick together, and it takes a lot of energy to make the molecules vibrate.

  32. Water has a specific heat of 4186 J/kg*K. If 6,000 J of energy are added to 50 kg of water, how much will the temperature change? • .023 K

  33. Lots of energy needed to get water hot

  34. End of notes day 2

  35. Notes, day 3

  36. Objectives for DAY 3: • 10. Be able to solve word problems involving relationships defined in this unit. • 11. Use the concept of Calorimetry to determine the specific heat capacity of an unknown in a lab situation. • 12. Describe some of the factors that can lead to a large or small Latent Heat

  37. Calorimetry: is used to determine c of a substance. • By putting a hot object into water, the change in the temperature of the water can be measured and can be used to find c of the substance.

  38. Uwater = -Usubstance • c*m*deltaT(water) = - c*m*deltaT(substance)

  39. Page 315, Sample Problem C (Do together)

  40. Latent Heat: The energy per unit mass that is transferred during a phase change of a substance.

  41. U = m*L (L = latent heat)

  42. Water has very large latent heat values due to its hydrogen bonds. • Octane does not have a very large latent heat value because its molecules do not stick together strongly compared to water.

  43. The energy change needed for a substance to change from liquid to solid (or vice versa) is called the Latent Heat of Fusion. • The energy change needed for a substance to change from liquid to gas(or vice versa) is called the Latent Heat of Vaporization.

  44. Link to specific heat data: http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html

  45. End of notes, day 3

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