Heat and Temperature

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Heat and Temperature
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Temperature

• Temperature measures the speed of the molecules
• Celsius Scale
• 00C water freezes, 1000C water boils
• Fahrenheit Scale
• 320F water freezes, 2120F water boils
• Kelvin Scale0K
• 2730K water freezes, 3730K water boils
• ABSOLUTE Zero 00K

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First Law of Thermodynamics

• The first law of thermodynamics is the
  application of the conservation of energy
  principle to heat and thermodynamics

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Enthalpy

• Enthalpy is a quotient or description of
  thermodynamic potential of a system, which can be
  used to calculate the heat transfer
• H U(internal energy) pV (pressure Volume)
• The new variables often make the analysis of a
  system much simpler. For a gas, a useful
  additional state variable is the enthalpy which
  is defined to be the sum of the internal energy U
  plus the product of the pressure p and volume V.
  Using the symbol H for the enthalpy .

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Entropy

• Entropy is central to the second law of
  thermodynamics
• that over time, ignoring the effects of
  self-gravity, differences in temperature,
  pressure, and density tend to even out in a
  physical system that is isolated from the outside
  world.
• Entropy is a measure of how far along this
  evening-out process has progressed.

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Heat

• Internal Energy of a system
• Q amount of heat in joules
• Specific Heat (c)
• Cal/grams (Chemistry/Earth Science)
• Joule per gram per 0C (Physics)
• ( J/Kg 0C )

Formula Q m c D Tc
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Sample Problem

• How much heat is needed to raise the temperature
  of 30 kilograms of liquid water from 10 0C to 20
  0C ?

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Solution to heat problem

• Q m c D Tc (Physics)
• 30 Kg x 4.19 J/kg 0C x (20-10)0C
• 1,257J
• Q m c D Tc ( Earth Science Chemistry)
• 30,000 x 1.0 cal/g 0C x (20-10)0C
• 30,000 gm x 1.0 cal/g 0C x (20-10)0C
• 300,000 cal

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Changes in state
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Changes in State terms
Sublimation
Evaporation
Condensation
Melting
Freezing
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Heating and Changes in Phase
HVAC systems transfer energy using phase changes
to absorb and radiate HEAT
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Changes in State

• Heat of Fusion (Hf)
• Conversion from Solid Liquid
• Heat of Vaporization (Hv)
• Conversion from Liquid Gas
• Formula Q m Hf or m Hv
• Hf 80 cal/g or 334 J/g
• Hv 540 cal/g or 2260 J/g

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Change in State Graph
1. Copy this graph2. Identify specific heat,
heat of fusion, and heat of vaporization.
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Change in State Areas
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Calculate Heat of Fusion from a graph
Time in minutes
mass 2.0 kg rate of loss 2.0 kJ/minute
Q mHf 8,000 J 2,000 g Hf 4 J/kg Hf
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Boiling and Freezing Points
What is the boiling point?
140 degrees Celsius
60 degrees Celsius
What is the freezing point?
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Sample Heat of Fusion

• How much heat energy is needed to melt 5.0
  kilograms of water at its melting point?

Q m Hf (Physics) 5 Kg x 334 J/Kg
1,670J
Q m Hf (Earth Science) 5.0 kg x 80 cal/g
5000 g x 80 cal/g 400,000 cal
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Summary

• Temperature is a measure of the activity of
  molecules.
• Heat is a measure of energy
• Specific Heat determines the amount of energy
  that a substance stores
• Heat of Fusion or Vaporization is a measure of
  the energy stored in the physical state of matter