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HEAT

This guide covers the essentials of temperature conversion between Fahrenheit, Celsius, and Kelvin, providing formulas and steps for accurate calculations. Users will learn how to solve 2-step temperature equations, such as converting Kelvin to Fahrenheit and vice versa. Additionally, the guide introduces heat units, including joules, calories, and British thermal units (Btus), explaining their historical context and relationships. By mastering these concepts, students can effectively navigate both theoretical and practical applications of thermal science.

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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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