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 Show all work Put box around final answer
Solving 2–Step temperature equations Necessary only when converting: K to oF oF to K
Temperature Conversion Equations 4 equations to use: oF = 9/5oC + 32 oC = 5/9 (oF-32) K = oC + 273 oC = K – 273
Convert 500 K to ____ o F First convert K to o C Then convert C to o F Use this equation: oC = K – 273 Then convert C to o F Use this equation: oF = 9/5oC + 32
Convert 500 K to ____ o F oC = K – 273 oC = 500 – 273 oC = 227 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 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
oC = 5/9 (oF-32) oC = 5/9 (o70-32) oC = 0.55 (38) oC = 2.11 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
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:
Units of Heat
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)
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.
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
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
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
Calorimeters
Calorimeters (contd.)
Calorimetry: An Exercise in Bookkeeping
Calorimetry: Finding Specific Heats
Calorimetry: Specific Heat
Calorimetry: Mixtures
Water: Specific Heat Capacities and Latent Heats
Water: Warming Curve
Water: Example Problem
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
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
Phases of Matter
Latent Heat
Phase Diagrams
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
Phase Diagram: Water
Phase Diagram: Carbon Dioxide
Methods of Heat Transfer Objectives are to: describe the three methods of heat transfer Give practical/environmental examples of each
Thermal Conduction
Convection
Radiation Heat transfer by electromagnetic waves Does not need a material medium Black body: perfect absorber perfect emitter (at all wavelengths)
Radiation
Convection
Convection at Home
Convection
Greenhouse Effect
Greenhouse Effect
Heat Transfer
Radiation