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 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