Transcript Thermal Energy and Heat

Thermal Energy
and Heat
Kinetic Theory of
Matter
 ALL
particles that make
up matter are constantly
in motion.
 ALL particles in matter
have kinetic energy.
 Within a substance, not
all particles move at the
same rate.
Temperature
A
measure of the
average kinetic
energy of the
individual particles of
matter
 Depends on mass as
well as speed
Temperature
 Thermometer
is used
to measure
temperature
3
common scales
Fahrenheit
Celsius
Kelvin
Fahrenheit Scale
Most common in the U.S.
 32o = water freezes
 212o = water boils
 Intervals in between are
divided into 180 equal
intervals called degrees
Fahrenheit (oF)
 Absolute zero = -459
degrees

Celsius Scale
 Used in most of the
 0o = water freezes
 100o
world
= water boils
 Intervals divided into 100
equal parts called
degrees Celsius (oC)
 Absolute zero = -273
degrees
Kelvin Scale
 Most
commonly used in
physical science
 273 degrees = water
freezes
 373 degrees = water
boils
 Kelvin scale is designed
so that 0 = absolute zero
Conversion between Celsius
and Fahrenheit
Thermal Energy
 The
total energy of all
of the particles in a
substance or material
 The more particles a
substance has at a
given temperature; the
more thermal energy it
has
Thermal Energy
Example:
2L of
hot chocolate at
o
75 has more
thermal energy
than 1.5L of hot
o
chocolate at 75
Thermal Energy
 Thermal
energy depends
on:
temperature
 # particles in a substance
 how the particles are
arranged

Heat
 Movement
of thermal
energy from a
substance at a higher
temperature to
another at a lower
temperature
Heat
 When
energy flows
from one object to
another; the thermal
energy of BOTH
objects changes
 Ex: ice cube in bowl
Measuring Heat
 Calorie
 Amount
of energy needed
to raise the temp. of 1g of
water by 1 degree Celsius
 Joule
 SI
unit for energy
 One calorie = 4.18J
Measuring Heat
1
C = 1kilocalorie (1000
calories)
 Each calorie of food
contains 1000 calories
of energy
 Measured by a
calorimeter
Specific Heat
A quantity to measure the
relationship between heat
and temperature change
 Amount of energy required
to raise the temperature of
1g of a substance by 1oC
 Every substance has its own
specific heat

Heat Transfer
3
ways heat can be
transferred:
 Conduction
 Convection
 Radiation
Conduction
 Heat
is
transferred
without the
movement
of matter
itself
 Heat is
transferred
by touching
Convection
Transfer
of heat by
the movements of
a fluid
Gas or liquid
Convection Current
 Movement
of a fluid
caused by differences
in temperature
Radiation
 Transfer
of energy by
electromagnetic waves
 Feel radiation from a
bonfire; heat lamp
 DOES NOT require
matter to transfer
thermal energy
Heat Transfer
 Heat
flows into a
substance; thermal energy
increases; as thermal
energy increases,
temperature increases
 Heat will flow until 2
substances have same
temperature
Heat Transfer
Example:
ice
cream
Heat from
ingredients flows
to the ice
Conductors
A
material that
conducts heat well
Metals: silver,
copper, stainless
steel
Insulators
A
material that does
not conduct heat
well.
Wool, straw, paper,
cork
Gases: air
Changes in State
Three
states of
matter
Solid
Liquid
Gas
Changes in State
 Physical
change is a
change of state from one
form to another
 Most often occurs
between solid & liquid;
liquid & gas
Changes in State
 Matter
will change
from one state to
another if thermal
energy is absorbed
or released.
Changes in State
 The
addition or loss of
thermal energy changes
the arrangement of the
particles.
 The average kinetic
energy DOES NOT
change.
Changes in State
 Melting:
solid to
liquid
 Melting point:
temperature at which
a solid changes to a
liquid
Changes in State
 Freezing:
liquid to a solid
 Freezing point: when a
substance loses thermal
energy; temperature at
which a liquid changes to
a solid
Changes in State
 Vaporization:
liquid to a
gas
 Evaporation:
at the
surface
 Boiling: below the surface
 Boiling point: temperature
at which liquid becomes a
gas (boils)
Changes in State
 Condensation:
becomes liquid
gas
Changes in State
 Thermal
Expansion:
expanding of matter when
it is heated
 As
thermal energy of a
substance increases, its
particles spread out.
 True even when a
substance is not spreading
out
Changes in State
 Examples
of thermal
expansion:
 Thermometer
 Teeth
(fillings)
 Thermostats (heatregulating device)
Uses of Heat
 Heat
engine
 Conversion
of thermal
energy to mechanical
energy requires a heat
engine
 Make use of
combustion: burning
fuel (coal, gasoline)
Heat Engine
 During
combustion,
chemical energy is
converted to thermal
energy
 Heat engine converts the
thermal energy into
mechanical energy
Heat Engine
 Classified
according to
whether combustion
takes place outside the
engine or inside the
engine
Heat Engine
 External
combustion
engine
Fuel is burned
outside the engine.
Steam engine
Heat Engine
 Internal
combustion
engine
 Fuel
is burned in
cylinders inside the
engine
 Automobiles