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HEAT

HEAT. ConversionTemperatures :. Temperature Scales. Fahrenheit Celsius Kelvin. Helpful Hints. Identify the equation needed. Plug in the numbers to solve Remember the math rules: Solve what is in parenthesis first Solve Multiplication & Division before addition and subtraction

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HEAT

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  1. HEAT ConversionTemperatures:

  2. Temperature Scales • Fahrenheit • Celsius • Kelvin

  3. Helpful Hints • Identify the equation needed. • Plug in the numbers to solve • Remember the math rules: • Solve what is in parenthesis first • Solve Multiplication & Division before addition and subtraction • Show all work • Put box around final answer

  4. Solving 2–Step temperature equations • Necessary only when converting: • K to oF • oF to K

  5. Temperature Conversion Equations • 4 equations to use: • oF = 9/5oC + 32 • oC = 5/9 (oF-32) • K = oC + 273 • oC = K – 273

  6. Convert 500 K to ____ o F • First convert K to o C • Use this equation: oC = K – 273 • Then convert C to o F • Use this equation: oF = 9/5oC + 32

  7. Step 1: oC = K – 273 oC = 500 – 273 oC = 227 Step 2: oF = 9/5oC + 32 oF = 9/5(227) + 32 oF = 1.8(227)+ 32 oF = 408.6+ 32 oF = 440.60 Convert 500 K to ____ o F

  8. Convert 70 o F to ____ K • First convert o F to o C • Use this equation: oC = 5/9 (oF-32) • Then convert C to K • Use this equation: K = oC + 273

  9. Convert 70 o F to ____ K • Step 1: oC = 5/9 (oF-32) oC = 5/9 (o70-32) oC = 0.55 (38) oC = 2.11 Step 2: K = oC + 273 K = 2.11 + 273 K = 275.11

  10. Units of Heat Objectives are to: • define and distinguish between various units of heat • define the mechanical equivalent of heat • discuss everyday examples to illustrate these concepts Temperature Conversions:

  11. Units of Heat

  12. Units of Heat • Heat is energy in transit, and is measured in energy units. • The SI unit is the joule (J), or Newton-metre (Nm). • Historically, heat was measured in terms of the ability to raise the temperature of water. • The kilocalorie (kcal), or Calorie (Cal), or “big calorie”: amount of heat needed to raise the temperature of 1 kilogramme of water by 1 C0 (from 14.50C to 15.50C) • The calorie, or “little calorie”: amount of heat needed to raise the temperature of 1 gramme of water by 1 C0 (from 14.50C to 15.50C) • In industry, the British thermal unit (Btu) is still used: amount of heat needed to raise the temperature of 1 lb of water by 1 F0 (from 630F to 640F)

  13. Mechanical Equivalent of Heat Joule demonstrated that water can be heated by doing (mechanical) work, and showed that for every 4186 J of work done, the temperature of water rose by 1C0 per kg.

  14. Mechanical Equivalent of Heat • Conversion between different units of heat: 1 cal = 10-3 kcal = 3.969 x 10-3 Btu = 4.186 J 1 Cal = 1 kcal=4186 J

  15. Sensible Heat Objectives are to: • describe what is meant by 'sensible heat‘ • define specific heat • explain how the specific heat capacities of materials are obtained using calorimetry

  16. Specific Heat Capacity • Sensible heat is associated with a temperature change (can be “sensed”) • Different substances have different molecular configurations and bonding  temperature change not generally the same for equal amounts of heat • Specific heat capacity, c: amount of energy needed to raise the temperature of 1 kg of a substance by 1K

  17. Calorimeters

  18. Calorimeters (contd.)

  19. Calorimetry: An Exercise in Bookkeeping

  20. Calorimetry: Finding Specific Heats

  21. Calorimetry: Specific Heat

  22. Calorimetry: Mixtures

  23. Water: Specific Heat Capacities and Latent Heats

  24. Water: Warming Curve

  25. Water: Example Problem

  26. Latent Heat Objectives are to: • Describe what is meant by ‘latent heat‘ • Compare and contrast the 3 phases of matter • Relate latent heat to phase changes

  27. Phases of Matter • Heat required for phase changes: • Vaporization: liquid  vapour • Melting: liquid  solid • Sublimation: solid  vapour • Heat released by phase changes: • Condensation: vapour liquid • Fusion: liquid  solid • Deposition: vapour solid

  28. Phases of Matter

  29. Latent Heat

  30. Phase Diagrams

  31. Phase Diagrams • Visual representation of phase changes • Triple point: point at which all three phases coexist • Curves branching out from this point separate phase regions: • Fusion curve: solid-liquid boundary • Vaporization curve: liquid-gas boundary • Sublimation curve: solid-gas boundary

  32. Phase Diagram: Water

  33. Phase Diagram: Carbon Dioxide

  34. Methods of Heat Transfer Objectives are to: • describe the three methods of heat transfer • Give practical/environmental examples of each

  35. Thermal Conduction

  36. Convection

  37. Radiation • Heat transfer by electromagnetic waves • Does not need a material medium • Black body: perfect absorber  perfect emitter (at all wavelengths)

  38. Radiation

  39. Convection

  40. ConvectionatHome

  41. Convection

  42. Greenhouse Effect

  43. Greenhouse Effect

  44. Heat Transfer

  45. Radiation

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