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READ Chapter 9 & 10
Heat is energy in thermal form.
 Heat is the energy of moving molecules.
 Adding or removing heat changes the
temperature.

Example: Adding heat increases temperature.
 Heat has units of energy; Joules

A change in heat of an object is a change in energy of the
object.
 The concept of heat is based upon the
Kinetic Theory of Molecules
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Kinetic Molecular Theory
 Tiny particles (molecules) are always in
motion.
 At zero Kelvin, molecules stop moving.
 The faster the motion the hotter the body.
 Temperature - the AVERAGE kinetic energy
of the molecules of a body
 Energies of the atomic motion are internal
energies.
Thermal Energy
– The internal potential and kinetic energy in a body
Thermal Energy
Potential and Kinetic
Solid
Liquid
Gas
All Kinetic
Plasma
Temperature
As a substance changes states the molecular
interactions weaken and the potential energy
is turned into kinetic energy.
Typically as the temperature increases the matter changes states.
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Thermal Expansion
 Most materials change their dimensions when their
temperature changes.
 Matter, typically, expands as temperature increases.
 The expansion of materials with an increase in
temperature must be taken into account when making
structures, such as bridges or railroad tracks.
Thermal Expansion
 Thermal expansion is indicated by a quantity called
the coefficient of expansion.
 Gases have the largest coefficient of expansion.
 Remember most matter typically expands as
temperature increases so as temperature decreases
what should happen?
 H2O does not follow this rule.
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Temperature
 Celsius – Water freezes at 0° and boils at 100°
 was based on water
 C = K – 273
 The unit is °C
 Kelvin – Water freezes 273 and boils at 373
 used for very high or very low temperatures
 K = C + 273
 The SI unit is K
 Absolute Zero – where all molecular motion stops
Celsius, Fahrenheit, and Kelvin Temperature Scales
The reference points in Celsius, Fahrenheit, and Kelvin
Temperature scales are shown below:
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Heat Transfer
 All bodies exchange heat with their environment.
 Heat flows from hot to cold.
 Heat is transferred by the following processes:
• Conduction
• Convection
• Radiation
Conduction
 Heat conduction can be visualized
as the result of molecular collisions.
 Only takes place if there is a
difference in temperature
 Thermal Conductivity – property of
the material that shows how well a
material conducts heat
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Convection
 The process whereby heat is transferred by the
mass movement of molecules from one place to
another.
 Hot fluids are less dense than cool liquids so they
rise to the top. The cool sinks to the bottom.
 Examples:
 Natural – wind, ocean currents, blood
 Forced - radiator
Radiation
 Does not require matter to transfer energy
 Comes mainly from infrared radiation
(electromagnetic waves)
 A good absorber is also a good emitter.
 Examples: sun, fire, black body radiation
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States of Matter
 Solid – atoms exert forces on each other holding them in a
pattern.
 The forces are of an electrical nature which means that it is a
balance of attractive and repulsive forces.
 The molecules are moving – they tend to vibrate around a
spot.
 Liquid – the molecules are moving more rapidly making
the attraction between the molecules weaker allowing
them to move in a less structured manner.
 Gas – the molecules are moving fast at speeds so fast the
attraction forces are weak and the molecules do not stay
close to each other. On the average the speeds are so fast
that even when they collide the attractive force is not
strong enough to hold them together.
Phase Changes
 Heat (Q)- the transfer in thermal energy, measured
in Joules. Always flows from hot to cold.
 Thermal Energy – the combined potential and
kinetic energy of the molecules in a substance
 Phase changes involve potential energy between
particles. There is NO temperature change while a
substance is changing phases
 Latent Heat – Energy transferred as heat during a
phase change.
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Latent Heat
 To have a ‘Change of phase’ requires energy
 Latent heat is the energy required to change from
one state to an other. The temperature of the
substance DOES NOT change until the phase
change is complete.
 Heat of Fusion – LF – solid to liquid
 Heat of Vaporization – LV – liquid to gas
Heat and Work
 Work is the change in Kinetic Energy. Total energy of
a system is always conserved.
 Fd=W= DKE
 DU + DK + DEi = 0
 Textbook uses DKE + DPE + DU = 0
 W = Q (if there are no outside forces)
 Q=mCPDT
 m = mass
 CP = specific heat in J/(kg°C)
 DT = change in temperature in °C
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Specific Heat
 If heat is put into a system the temperature will rise
 Q = mCPDT
 CP = specific heat
 The larger the specific heat the more energy is needed
to change the substance temperature.
Specific Heat Capacity
 Specific Heat capacity is the amount of energy it takes
to raise 1 kg of a substance 1 °C.
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Thermal Equilibrium
 When the objects in a system are at the same
temperature the system is in THERMAL
EQUILIBRIUM
 When the objects have different temperatures heat
flows until thermal equilibrium is reached.
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