heat
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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– 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
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 CUse this equation: oC = 5/9 (oF-32)
Then convert C to KUse this equation: K = oC + 273
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 + 273K = 2.11 + 273K = 275.11
Units of HeatObjectives are to: define and distinguish between various units of heat define the mechanical equivalent of heat discuss everyday examples to illustrate these
conceptsTemperature 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 ConductionQ TkAt d
Convection
Radiation
Heat transfer by electromagnetic waves Does not need a material medium Black body: perfect absorber perfect
emitter (at all wavelengths)
4 4
4 4
r a env
net a r env
P A T P A T
P P P A T T
Radiation
Convection
ConvectionatHome
Convection
Greenhouse Effect
Greenhouse Effect
Heat Transfer
Radiation