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Heat, Temperature, Heat Transfer, Thermal Expansion

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Heat, Temperature, Heat Transfer, Thermal Expansion & Thermodynamics Heat vs. Temperature Heat A form of energy Measured in calories or Joules There is no coldness ... – PowerPoint PPT presentation

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Title: Heat, Temperature, Heat Transfer, Thermal Expansion


1
Heat, Temperature, Heat Transfer, Thermal
Expansion Thermodynamics
2
Heat vs. Temperature
  • Temperature
  • Avg. Kinetic Energy of the particles
  • Measured in ?C, ?F, K
  • hot cold are relative terms
  • Absolute zero is zero Kelvin
  • Heat
  • A form of energy
  • Measured in calories or Joules
  • There is no coldness energy
  • Any object with temperature above zero Kelvin has
    heat energy

3
Heat Transfer
  • Conduction - requires direct contact or
    particle to particle transfer of energy usually
    occurs in solids
  • Convection - heat moves in currents hot
    air rises and cold air falls only occurs in
    fluids (liquids and gases)
  • 3.Radiation electromagnetic (heat) waves travel
    through empty space, no matter is needed sun

4
Thermal Equilibrium
  • A system is in thermal equilibrium when all of
    its parts are at the same temperature.
  • Heat transfers only from high to low temperatures
    and only until thermal equilibrium is reached.

5
Temperature Scales
  • There are four temperature scales Celsius
    (Centigrade), Kelvin, Fahrenheit
  • Celsius, ?C metric temp. scale
  • Fahrenheit, ?F customary (english) temp. scale
  • Kelvin, K metric absolute zero temp. scale
  • Rankine, R english absolute temp. scale

6
Comparing Temperature Scales
(All temperatures listed are for water)
  • Freezing 0C 273 K 32F
  • Boiling 100C 373 K 212 F

Conversions between Scales
F 1.8 xC32 9/5 C 32 C (F 32)
/ 1.8 5/9 (F 32) K C 273 or C K -
273
7
Change of State
steam
vaporization
Heat of fusion
100
condensation
water
Temp C
melting
Heat of vaporization
0
ice
freezing
-20
Increasing Heat Energy (Joules)
As heat is added to a substance it will either be
absorbed to raise the temperature OR to change
the state of matter. It can NEVER do both at the
same time! Temperature will NOT change during a
phase change!
8
Specific Heat
The amount of heat energy needed to raise the
temperature of 1 gram (or kg) of a substance by
1C (or 1 K). Substances with higher specific
heats, such as water, change temperature more
slowly.
Symbol c units cal/(gC) or J/(kgC)
For water c 4.186 J/(gC) 4186 J/(kgC)
or c 1 cal/ (gC)

9
Latent Heat
(Latent) Heat of fusion the heat energy
needed to melt (solid?liquid) or freeze (liquid ?
solid) one gram (or kg) of a substance.

For water Hf 334,000 J/kg or 80 cal/g
(Latent) Heat of vaporization the heat energy
needed to vaporize (liquid?gas) or condense
(gas?liquid) one gram (or kg) of a substance.
For water Hv 2.26
x 106 J/kg or 540 cal/g
10
Heat Calculations
Temperature Change
Phase Change
Q mHf Q mHv
Q mc?T
Q heat absorbed or released m mass of
substance changing phase, kg Hf heat of fusion,
J/kg (liquid solid) Hv heat of
vaporization, J/kg J/kg (liquid
gas)
Q heat absorbed or released, J m mass of
substance being heated, kg c specific heat of
substance, J/(kgC) ?T change in
temp.,C or K
11
Melting Boiling Point
  • Melting or Freezing Point the temperature at
    which a substance melts or freezes. Water 0C
  • Boiling or Condensation Point the temperature
    at which a substance vaporizes or condenses.
    Water 100C
  • For other substances, refer to your chart.

12
Thermal Expansion
  • Substances expand as they heat and contract as
    they cool.
  • The rate of expansion depends on the substances
    coefficient of expansion ( a for linear, ß for
    volume)
  • The exception to this rule is water. As water is
    cooled from 4C to 0C, it expands which explains
    why ice floats (it is less dense than water).

13
ThermodynamicsThe study of changes in thermal
properties of matter
14
0th Law of Thermodynamics
  • Heat will be transferred between objects until
    thermal equilibrium (same temperature) is reached.

15
1st Law of Thermodynamics
  • Conservation of energy
  • Energy can not created or destroyed but can
    change forms.
  • Thermal energy can be transferred from one
    substance to another.

16
2nd Law of Thermodynamics
  • Natural (spontaneous) processes tend to increase
    the total entropy (disorder) of the universe.
  • Entropy increases when heat is added to a body
    and decreases when heat is removed.
  • Heat flows naturally from a hot body to a cold
    body.

17
3rd law of Thermodynamics
  • As the temperature of an object approaches
    absolute zero (0 Kelvin), its entropy and kinetic
    energy approach zero.
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