Transcript 1. Heat Transfer - Science Fiction

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Do Now
•Write down three thing
you need to do to work
safely in a science
laboratory
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SPECIFIC HEAT CAPACITY
Outcomes:
• Understand that different materials require
different amounts of energy to increase their
temperature.
• Know the equation.
• Be able to use the equation.
• Be able to describe an experiment to measure heat
capacity.
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Copy this Glossary
 absorber – A material that takes in thermal radiation.
 conduction – The method of heat transfer in solids.
 conductor – A material that lets heat flow through it.
 convection – The method of heat transfer in fluids, which
occurs because hot fluids are less dense than cold fluids.
 emitter – A material that gives out thermal radiation.
 free electrons – Electrons in a metal that are free to move
through the metal.
 heat transfer – The flow of heat energy from a hotter area
to a colder area.
 radiation – Heat energy transferred by infrared waves.
This method of heat transfer does not need particles.
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How does energy affect materials?
Do different materials need the same amount of energy to
increase their temperature by the same amount?
To increase the
temperature of 1 kg
of water by 1°C,
requires 4200 J.
To increase the
temperature of 1 kg
of copper by 1°C,
requires 390 J.
Water and copper require different amounts of energy
because they have different values for a property called
specific heat capacity.
It is the amount of energy required to increase the
temperature of 1 kg of a material by 1°C.
So, the specific heat capacity for water is 4200 J/kg°C
and for copper is 390 J/kg°C.
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What is specific heat capacity?
The specific heat capacity of a material is the amount of
energy required to raise 1 kg of the material by 1 °C.
It can be used to work out how much energy is needed to
raise the temperature of a material by a certain amount:
specific heat
temperature
energy = mass x
x
capacity
change
 Energy is measured in joules (J).
 Mass is measured in kilograms (kg).
 Temperature change is measured in °C.
 Specific heat capacity is measured in J/kg/°C.
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Calculations using S.H.C.
Energy absorbed = Mass x Specific Heat capacity x Temp rise
J
kg
J/kg/°C
°C
The Mr McT equation
E = mcΔT
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For example
0.5 kg of olive oil is heated until its temperature rises
by 120 K. If the specific heat capacity of olive oil is
1970 J/kg/°C, how much heat energy was used?
Energy absorbed = Mass x Specific Heat capacity x Temp rise
Energy absorbed = 0.5 x 1970 x 120
Energy absorbed = 118200 J
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Practical
A
12V
V
A metal
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Go through Practical
worksheet
Follow instructions.
Take measurements and do
calculations.
All students must complete
the lab sheet
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Measuring SHCs
• Energy put IN to metal = voltage x current x time
• Energy = mass x specific heat capacity x temp rise
voltage x current x time = mass x specific heat capacity x temp rise
Specific heat capacity = (voltage x current x time)/(mass x temp rise)
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Specific heat capacity example
Using the specific heat capacity
of water (4200 J/kg°C), how much
energy is needed to increase the
temperature of 600 g of water by
80°C in a kettle?
Note: mass = 600 g = 0.6 kg
specific heat
temperature
energy = mass x
x
capacity
change
energy = 0.6 x 4200 x 80
= 201 600 J
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Do now
Specific heat
questions
Q5 June 2005
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Latent heat
Learning today
• Use the terms latent heat of fusion
and give a molecular interpretation of
latent heat
• Describe an experiment to measure
specific latent heats for ice
• Test Sunday 1st April 2012
• I will collect your books on Monday
Latent Heat
Latent heat
In a change of state experiment, from the graph you
will notice a flat spot the temperature of the salol
stopped changing as the salol changed from a liquid
to a solid.
Temp
(°C)
Melting point
Time (mins)
Specific Latent heat
“latent” = “hidden”
Why does
this
happen?
Specific Latent heat - Copy
When a substance changes from solid to liquid or from
liquid to gas, it takes energy to change its state.
Heat is needed to break the bonds or separate the
molecules. The temperature remains the same.
When a liquid changes back to a solid energy is released
again as the bonds form again.
liquid
Temp
(°C)
Melting point
solid
Time (mins)
solid to liquid increasing their potential energy instead of raising the temperature (kinetic energy
Specific Latent heat - copy
The specific latent heat of a substance
tells us how much energy is needed to
change the state of 1 kg of substance
at constant temperature.
Solid to liquid/liquid to solid
or
liquid to gas/gas to liquid
Specific Latent Heat
The specific latent heat of fusion (melting) of ice at 0
ºC, for example, is 330000 J.kg-1. This means that to
convert 1 kg of ice at 0 ºC to 1 kg of water at 0 ºC,
330000 J of heat must be absorbed by the ice.
All at 0°C
1 kg
1 kg
334000 J absorbed
Specific Latent Heat
Conversely, when 1 kg of water at 0 ºC
freezes to give 1 kg of ice at 0 ºC, 330000 J
of heat will be released to the surroundings.
1 kg
1 kg
330000 J released
All at 0°C
Specific Latent Heat -Copy
Energy = mass x specific latent heat
J
kg
E = mL
J/kg
Specific Latent heat L
E=mL
Do Now
question 1
page 119
Learning today
• Use the terms latent heat of fusion
and fusion and give a molecular
interpretation of latent heat
• Describe an experiment
to measure specific latent heats
for ice and steam
• Test Sunday 1st April 2012
• I will collect your books Today
Specific Latent Heat of Fusion
Experiment
•
•
•
•
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•
•
Readings required
Energy supplied by heater
Energy = Power x time
Time =
Energy = VIt
Mass of water
E = mL
• Latent heat = Energy supplied
.
mass of water
Specific Latent Heat of Fusion
Experiment
• Energy = Power x time
• Time =
• Energy = VIt =
• Mass of water =
• E = mL
• L = E /m
• Latent heat = Energy supplied
.
mass of water
Task- Evaluation
• What are the limitations in our method?
• What solutions can you think of?
• Why do we wait until the water is
dripping?
• Does all the heat come from the heater?
• Does all the ice remain in the funnel?
• Now do Q4 Nov 2005
4
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Markscheme
(a)
turn on heater and wait until water starts dripping in beaker
empty beaker & replace, start watch
stop watch & remove beaker at same time
record time
find and record mass of water in beaker
(b) 60 x t = 120 x 340
t = 680 s
(c) (i) ice gains heat from surroundings/ice falls through funnel
(ii) lag or fit lid to funnel/place gauze in funnel bottom
Specific Latent Heat of Fusion
Experiment
Latent heat
Now do
Nov 2005
Q5
Specific Latent Heat of
Vaporisation - Copy
For water at its normal boiling point of 100 ºC, the latent
specific latent heat of vaporisation is 2260000 J/kg. This
means that to convert 1 kg of water at 100 ºC to 1 kg of
steam at 100 ºC, 2260000 J of heat must be absorbed by
the water.
vice verse for vapour to liquid
All at 100°C
1 kg
1 kg
2260000 J input
Specific Latent Heat of
Vaporisation
Conversely, when 1 kg of steam at 100
ºC condenses to give 1 kg of water at
100 ºC, 2260 kJ of heat will be released
to the surroundings.
All at 100°C
1 kg
1 kg
2260000 J released
Specific Latent Heat of Steam
Latent Heat
Specific Latent Heat -Copy
Energy = mass x specific latent heat
J
kg
E = mL
J/kg