IGCSE Coordinate Science 1
Thermal Energy
P5, P6, C6 Key Notes
Review
• List the three major states of matter &
brainstorm everything you can remember
about each one.
Expansion
• Many substances expand when heated
• When heated, the particles (atoms or
molecules) in a substance gain Kinetic
Energy so they vibrate more
• This means they need more space
• So the substance expands
Heat
Important note!
The particles in a substance do not expand
themselves!
Heat
Particles are the same size
Contraction
• The opposite happens when most
substances are cooled
• The particles vibrate less
• They need less room
• The substance contracts
Cools
Solids
• The expansion of solids is small but strong!
Like me!
Expansion in solids
This means that we sometimes have to take
into account expansion
Expansion in solids
This means that we sometimes have to take
into account expansion
Real Life Expansion
• https://www.youtube.com/watch?v=WEfu4HyyLw
Contraction can also be a problem
Liquids
• Most liquids expand when heated
Gases
• Gases expand a lot
when heated!
• http://www.youtube.com/watch?
v=A843PL6Yejs&feature=related
• http://www.youtube.com/watch?
v=ZgTTUuJZAFs&feature=relat
ed
Boyle’s Law
• Review – What was Boyle’s law?
– The volume of a fixed mass of gas is inversely
proportional to its pressure, provided its
temperature remains constant.
• So what if gasses are heated? What will
happen to its volume if pressure remains
constant?
Temperature and volume of a gas
at constant pressure
• When gas is heated (at constant pressure) the
gas expands.
• http://phet.colorado.edu/en/simulation/gasproperties
Investigating Ice (Water)
• Measure (or zero) the mass of a glass beaker.
• Place at least 50 g of ice cubes in the beaker.
Measure the mass of the ice cubes.
• You will be investigating temperature vs. time
as ice melts.
– Measure the initial temperature of the ice (time = 0 s)
– Using the hot plate, heat the beaker. Measure and
record the temperature every 30 seconds until all the
water has evaporated.
• Create a temperature vs. time graph.
Thermal Capacity
• Thermal Capacity: Amount of heat required
to change a substance’s temperature by a
given amount.
– The higher the thermal capacity, the more heat an
object must absorb to increase its temperature.
– Dependent on what the material is made of
– Objects such as wood, glass, and plastic have
higher thermal capacities compared to metals
such as iron and aluminum.
Specific Heat Capacity
• Specific Heat Capacity : the energy required
to raise the temperature of 1kg of substance
by 1oC.
• Different substances have different specific
heat capacities.
Specific Heat Capacity
Energy = mass x specific heat capacity x change in temperature
Q = mcΔT
• Where
– Q = energy in J
– M = mass in kg
– C = specific heat capacity in J /kgoC
– ΔT = Tfinal – Tinitial (both in oC)
Examples
• 1. Water has a specific heat capacity of
4200 J/kgoC while sand has a specific heat
capacity of 1381 J/kgoC. What does this
mean?
• 2. A hot water tank contains 200kg of water
at 20oC. How much energy must be supplied
to heat this water to 70oC? The specific heat
capacity of water is 4200 J/kgoC .
Phase Change
http://cnx.org/contents/5f2b5aef-4948-488f-8ff9-839478a6d6cf@8/Phase_Change_and_Latent_Heat
Melting/Fusion and Boiling/Vaporization
http://cnx.org/contents/5f2b5aef-4948-488f-8ff9-839478a6d6cf@8/Phase_Change_and_Latent_Heat
Latent Heat
• Latent Heat of Fusion – the amount of heat
needed to change the state of 1kg of
substance from solid to liquid (or vice versa)
– Lf = 340,000 J/kg
(latent heat of fusion of water)
• Latent Heat of Vaporization – the amount of
heat needed to change the state of 1kg of
substance from liquid to gas (or vice versa)
– Lv = 2,300,000 J/kg
(latent heat of vaporization of water)
Evaporation vs. Boiling
March 01
ration
vs.
Boiling
• Evaporation is not boiling. It is the escape of
more energetic molecules from the surface of a
h are changes
liquid. of the state of matter
m liquid
to gas
• With
boiling, evaporation is very rapid as vapor
bubbles
throughout
quid boils
at itsform
boiling
point, butthe liquid, rise to the
top,happens
and burstat–areleasing
poration
lower large amounts of vapor.
perature, below the boiling point.
March 01,
Methods of Heat Transfer - 1
Methods of Heat Transfer
- heat transfer between solids
•1.)1.Conduction
Conduction
– heat transfer between solids.
Molecules
in amolecules
solid are very
closeare
to each
*–Recall
that the
in solids
very other.
oneother.
part of
a solid
closeWhen
to each
When
oneobject,
part ofsay
thea metal
solidspoon,
object,issay
a metal
the will be
heated,
thespoon
other istipheated,
of the spoon
otherhot
tip after
of thesome
spoon
will be hot after some
time.
time.
Types of Materials:
Conduction
Types of Materials:
•
•
a.) Conductors - ma
Typesa.)ofConductors
Materials:- materials that allowheat to transfer -rapid
me
heat to transfer
rapidly. that allowexamples
a) Conductors
– materials
heat toof conduc
- metals are very good
transfer
rapidly.
examples
of conductors
– Metals are good examples
of conductors.
b.) Insulators - mate
rapidly allow heat to
- wood
Insulators
–
materials
that
do
not
rapidly
b.) Insulators - materials that do notvery good examples
• b)
allowrapidly
heat to
transfer.
allow
heat to transfer.
- wood
and examples
plastics are
– Wood and plastics
are good
very good examples of insulators
of insulators.
Methods of Heat Transfer - 2
2.) Convection - heat transfer between
2.) Convection - heat
transfer
between
fluids
and gases)
• 2. Convection – heat(liquids
transfer between
fluids
(liquids and gases)
(liquids and gasses)
Methods of Heat Transfer - 3
• 3. Radiation –
energy spreading
out from a source
carried by particles
or waves
– The hotter the
object, the more
infrared radiation it
gives out.
Th
ob
in
it
urce carried by particles or waves
it gives out.
The hotter the
object, the more
infrared radiation
it gives out.
Good Absorbers, Good E
Good Absorbers, Good Emitters
It is the surface that
• It is the surface thatan
determines
whether an
object absorbs
or refle
object absorbs or reflects
infrared radiation.
radiation.
• A surface that is a good reflector is a poor
absorber.
• Matt black surfaces
are the best
absorbers and
best emitters
(the worst reflectors).
Home Insulation
Home Insulation
• Where
Where
the
doesdoes
the heat
go?heat go?
cavity walls
cavity walls
conduction
reduces heat los
conduction
heat
losses
foam or rockwool further reduces
rockwool by
further
losses
foam
orreduces
rockwoolheat
further
reduces
convection
in foam
wall or
cavity
Ways of Retaining Energy in a House
Ways of Retaining
Energy
incavity
a House
by convection
in convection
wall
in wall cavity
by
Method
Why it Works
stops convection currents,
thick curtains,
and so prevents cold air
draught excluders from entering and warm
air from leaving
loft and underfloor prevents conduction of
insulating
heat through floors and
ceilings
materials
double and triple
glazed windows
vacuum between glass
panes, cuts out losses by
conduction and convection
cavity walls
reduces heat losses by
conduction
foam or rockwool further reduces heat losses
by convection
in wall cavity
Endothermic and Exothermic
• Follow the instructions at each station
carefully and be sure to clean up after
yourself! Stay at the station until the buzzer
sounds.
• Be sure to record measurements and
observations when prompted!
Endothermic and Exothermic
• Read pages 114 - 116, then review each
demonstration and decide if the reaction was
endothermic or exothermic. Be sure to cite a
reason why!
• Define exothermic & endothermic.