Transcript HEAT AND TEMPERATURE

:
Comprehending states of matter and its
change
 Describe role of heat in changes
 states of matter and temperature’s substance
also its application in daily life
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5
• Before the 9th century, many scientist
believed that heat was a fluid.
• Heat as fluid firstly stated by Antoine
Laurent Lavoisier, He said that when a
hotter object was in contact with the
colder object, then the fluid would flow
• Some scientist disagreed with the concept
of Heat as fluid. Those scientist proved that
Heat was not a fluid, but a form of Energy
Antoine Lavoiser
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Heat energy is the total energy of particles composing a
matter.
Heat is one form of energy which is flowing from an object with
higher temperature to another object with lower temperature
The unit of Heat is Joule (J)
Heat is also expressed in units of calories.
One calorie defined as the amount of heat needed to heat 1
gram of water until its temperature increasing 1 C °.
1 calorie = 4.2 joules
1 joule = 0.24 calories
Heat Transfer
• Heat always moves from a warmer place to
a cooler place.
• Hot objects in a cooler room will cool to
room temperature.e.g: tea, coffee
• Cold objects in a warmer room will heat up
to room temperature.e.g: butter, ice
What do you think?
Heat Transfer
Conduction
Convection
Radiation
Radiation
How does heat energy get
from the Sun to the Earth?
?
There are no particles between the
Sun and the Earth so it MUST travel by
radiation
RADIATION
Radiation
• The transfer of heat in rays, from a
hot object, without needing a
medium to pass through
• It travels in all directions from a hot
object
• The hotter an object is, the more
heat it will radiate out
• Does the surface affect the way
heat is radiated?
 What colour should we paint
radiators?
Which colour is better to wear
on a sunny day?
black or white?
• A dull black surface will radiate and absorb
heat better than a bright shiny surface.
Four containers were filled with warm water. Which container
would have the warmest water after ten minutes?
Dull metal
Shiny metal
Shiny black
Dull black
shiny metal
The __________
container would be the warmest after ten
radiation back
minutes because its shiny surface reflects heat _______
dull black
into the container so less is lost. The ________
container would
emitting
be the coolest because it is the best at _______
heat radiation.
Radiation – Think Pair-Share
Radiation travels in straight lines
True/False
Radiation can travel through a vacuum
True/False
Radiation requires particles to travel
True/False
Radiation travels at the speed of light
True/False
Radiation questions
Why are houses painted white in hot countries?
White reflects heat radiation and keeps the house cooler.
Why are shiny foil blankets wrapped around marathon
runners at the end of a race?
The shiny metal reflects the heat
radiation from the runner back in,
this stops the runner getting cold.
Conduction
• Transfer of heat is through a SOLID by
being passed from one particle to the next
• Particles at the warm end move faster and
this then causes the next particles to move
faster and so on. e.g: poker in fire
spoon in tea
• In this way heat in an object travels from:
the HOT end
the cold end
Conduction
• When you heat a metal strip at one end, the heat travels to
the other end.
• As you heat the metal, the particles vibrate, these
vibrations make the adjacent particles vibrate, and so on
and so on, the vibrations are passed along the metal and
so is the heat. We call this? Conduction
Conductors/Insulators
• If a substance easily allows heat to move
through it, we can say it is a good
conductor of heat. e.g: most metals
• If a substance does not allow heat to pass
through it easily we can say it is an
Insulator. E.g: wood, plastic, glass
• Why do many sauce pans have plastic
handles?
Conduction V Insulation
Conductor or Insulator?
•
•
•
•
•
•
•
•
Wood?
Aluminium?
Plastic?
Glass?
Iron?
Polystyrene?
Copper?
Cardboard?
Convection
What happens to the particles in a liquid or a gas
when you heat them?
The particles spread out and
become less dense.
A liquid or gas.
Convection
• It is the way in which
particles in a GAS or LIQUID
move upwards, carrying heat
with them
• Think about when you boil water,
the bubbles move upwards
• Or think of a gas heater in the
room, the heat rises around the
room
Convection
Cools at the
surface
Cooler
water sinks
Convection
current
Hot water
rises
Convection
Where is the
cooling
compartment
put in a fridge?
It is put at the
top, because
cool air sinks,
so it cools the
food on the
way down.
It is warmer at the
bottom, so this
warmer air rises and
a convection current
is set up.
Should a radiator be called a
radiator?
Convection questions
Why does hot air rise and cold air sink?
Cool air is more dense than warm air, so the
cool air ‘falls through’ the warm air.
Why are boilers placed beneath hot water
tanks in people’s homes?
Hot water rises.
So when the boiler heats the water, and the hot
water rises, the water tank is filled with hot water.
of temperature
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Not all substances have the same ability in absorbing
heat.
The ability to absorb heat determined by the nature of
a substance called specific het capacity.
Specific Heat Capacity (c)
The specific heat capacity of a substance is
defined as the heat required to raising the
temperature of 1 kg of the substance by 1°C.
The unit of specific heat capacity is joule per kilogram
per Celsius degree (J/kg C°)
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This proved that heat needed to raise the
temperature of 1C ° alcohol is smaller
than the heat needed to raise water
temperature at 1C°. That is, alcohol heat
faster than water.
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The amount of heat (Q) required by an object is proportional to
the mass of the object (m), depending on the specific heat capacity
(c), and comparable to the increase in temperature(∆T).
The change of heat (received heat or released heat) of a
substance cannot be measured directly, but it can be calculated
using the following equation.
Q = m x c x ΔT
Notes:
Q = heat received or released (Joules)
m = mass (kg)
c = specific heat capacity (J/kg C°)
ΔT = changes of temperature (C°)
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Calculate heat needed to increasing temperature of 500 g
water from 20 ° C to 100 ° C,if the specific heat of water is
4200 J/ kg C°?
Given:
m= 500 g =0.5kg
c = 4200 J/kg C°
∆T = 100°C - 20°C = 80 C°
Question: Q = …?
Answer:
Q = m x c x ∆T
= 0.5 kg x 4200 J/kgC° x 80 C°
= 168,000 J
So the heat received by the water is 168,000 J
The heat capacity of a substance is defined as
the amount of heat required to raise its temperature
by 1 C°
Unit of Heat capacity is Joules per Celsius degree (J/C °)
Heat capacity can be calculated using the following equations.
C = m×c
Q
C=
∆T
Notes:
C = Heat capacity (J/C°)
m = mass (kg)
Q = heat received or released (Joules)
c = specific heat capacity (J/kg C°)
∆T = changes of temperature (C°)
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Answer these following questions!
1. Two containers of the same size are filled with water and sand
respectively. If they are exposed to the sun heat, which one gets
hotter more quickly? Why?
2. You’re heating a 3.0 kg glass block, specific heat capacity of 840
J/(kg.C °), raising its temperature by 60C°. What heat do you have
to apply?
3. 2 kg of iron is heated from 15 °C to 30°C. If the heat required is
13,500 J, what is specific heat capacity of iron?
4. 42 kilojoules of heat released from the 2 kg of ice at temperatures 15 ° C. What is the temperature finally, if the specific heat of ice
is 2100 J/kg. C°
5. To raise the temperature of an object from 10°C to 40°C, it
required heat 60,000 J. Calculate the heat capacity of its object!
• When a matter change its state, the
temperature does not increase although the
heat is continuously given.
• The heat is used to changing the state of matter.
• The heat used for changing the state of matter is
calledLatent heat.
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STATES OF MATTER
SOLIDS
•Particles of solids are
tightly packed, vibrating
about a fixed position.
•Solids have a definite
shape and a definite
volume.
Heat
STATES OF MATTER
LIQUID
 Particles of liquids are
tightly packed, but are
far enough apart to
slide over one another.
 Liquids have an
indefinite shape and a
definite volume.
Heat
STATES OF MATTER
GAS
 Particles of gases
are very far apart
and move freely.
 Gases have an
indefinite shape
and an indefinite
volume.
Heat
PHASE CHANGES
Description of
Phase Change
Solid to
liquid
Term for Phase Change
Melting
Liquid to
Freezing
solid
Heat Movement During
Phase Change
Heat goes into
the solid as it
melts.
Heat leaves the
liquid as it
freezes.
PHASE CHANGES
Description of
Phase Change
Liquid to gas
Gas to liquid
Solid to gas
Term for Phase
Change
Heat Movement During
Phase Change
Vaporization,
which includes
boiling and
evaporation
Heat goes into the
liquid as it vaporizes.
Condensation
Heat leaves the gas as
it condenses.
Sublimation
Heat goes into the solid
as it sublimates.
• Melting point is the temperature
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when a matter is starting to melt.
Example: melting point of ice is 0°C
• Freezing point is the temperature
when a matter is starting to freeze.
Example: freezing point of water is 0°C
Melting point = Freezing point
Melting
point
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The amount of heat absorbed by every 1 kg of matter for
melting at its melting point is called Melting heat (L).
The amount of heat released by 1 kg of matter for freezing at
its freezing point is called Freezing heat (L).
SI Unit of Melting Heat and Freezing Heat: J/kg
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AMOUNT OF HEAT (Q) RECEIVED OR RELEASED BY A MATTER
WHEN IT MELTS OR FREEZES
Where:
Q = amount of Heat received or released (J)
m = mass of matter (kg)
L = Melting heat or Freezing Heat (J/kg)
Boiling point is the temperature when a matter is
starting to boils.
Example: boiling point of water is 100ºC
Condensation point is the temperature when a
matter is starting to condenses.
Boling point = Condensation point
Boiling point of a liquid is affected by air
pressure
• The greater the air pressure the greater the
boiling point of liquid
• On the sea level, at air pressure of 1 atm, the Boiling
point
boiling point of water is 100 º C.
• At higher place, the air pressure is decrease
and boiling point of water is also decrease.
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The amount of heat absorbed by every 1 kg of matter for
vaporize at its boiling point is called vapouring heat (U).
The amount of heat released by 1 kg of matter for condense
at its condensation point is called condensation heat (U).
SI Unit of Vapouring Heat of Condensation Heat: J/kg
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AMOUNT OF HEAT (Q) RECEIVED OR RELEASED BY A MATTER
WHEN IT EVAPORATES OR CONDENSES
Where:
Q = amount of Heat received or released (J)
m = mass of matter (kg)
L = Vaporing Heat or Condensation Heat (J/kg)
Substance
Melting
point(ºC)
Helium
-269,65
Nitrogen
-209,97
Oxygen
-218,79
Ethylalcohol
-114
Water
0
Sulfur
119
Lead
Aluminum
327,3
660
Silver
960,8
Gold
1063
Copper
1083
Melting Boilingpoint VapouringHeat
Heat(J/kg)
(ºC)
(J/kg)
3
5,23x10
4
2,25x10
4
1,38x10
5
1,04x10
5
3,33x10
4
3,81x10
4
2,45x10
5
3,97x10
4
8,82x10
5
1,34x10
3
5,23x10
-268,93
-195,81
-182,97
78
100
444,6
1750
2450
2193
2660
1187
4
2,09x10
5
2,01x10
5
2,13x10
5
8,54x10
6
2,26x10
5
3,26x10
5
8,70x10
7
1,14x10
6
2,33x10
6
1,58x10
6
5,06x10
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No
Evaporation
Boiling
1.
Occursatanytemperature
belowboilingpoint
Occursatafixedtemperature
(boilingpoint)
2.
Occursontheliquid’ssurface
Occursthroughouttheliquid
3
Nobubblesareformed
Bubblesareformedinthe
liquid
4
SlowProcess
Quickprocess
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• Heating
– When we heated liquid, the molecules near the surface vibrate
faster, which enable them to release from liquid’s surface
• Blowing air through the liquid’s surface
– If we blow air through the surface of a hot water, the air near the
water surface would carry the water’s molecules at the surface.
• Extending the surface
– To make hot tea in a cup cold faster, you should pour on a saucer,
because the surface area of the saucer is larger than on the cup,
so the molecules have more chances to leave the water surface
• Decreasing the pressure on the surface
– If the pressure decreasing, the space between air molecules near
the surface become looser and it make easier for the molecules of
water to fill the empty space among the molecules of air.
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1. If ice melting, the state change from …. to …
2. For melting, ice …. heat energy
3. During ice melted, temperature is….. and it is
called …
4. Amount of heat energy used to melt you can
calculate
with the formula
5. During the water boil, the temperature is … and
it is called …
6. During the water boil, the state change from …
become … and is called …
7. During evaporation the water ……heat energy.
8. Quantity heat energy used to evaporation can
calculate by the formula …
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1. Calculate the quantity of heat required to melt 3 kg of ice
on 0ºC ! (L = 3.36 x 105 J/kg)
Known: m= 3 kg
L = 3.36 x 105 J/kg = 336,000 J/kg
Question: Q ?
Answer:
Q=mxL
Q = 3 kg x 336,000 J/kg
Q = 1,008,000 J = 1,008 kJ
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2. Calculate the quantity of heat required to change 500 grams
of water at a temperature of 100ºC into water vapor at a
temperature of 100ºC! (U = 2270 kJ/kg)
Known: m= 500 grams = 0.5 kg
U = 2270 kJ/kg
Question: Q
Answer:
?
Q=mxU
Q = 0.5 kg x 2,270 kJ/kg
Q = 1,135 kJ
Q = 1,135,000 J
3. Calculate the heat required to change 1 kg of water at 26
temperature of 80ºC into 1 kg of water vapor at a
temperature of 100ºC (specific heat of water is 4200 J/kgºC
and vapouring heat of water is 2270 kJ/kg)
Temperature
Known: m= 1 kg
∆T = (100-80) Cº = 20 Cº
c = 4200 J/kg Cº
U = 2270 kJ/kg = 2,270,000 J/kg
Question: Q total
Answer:
Q1 = m x c x ∆T
Q2
100ºC
Q1
80ºC
Q2 = m x U
Q total = Q 1 + Q 2
=(m x c x ∆T) + (m x U)
=(1 kg x 4200 J/kg Cº x 20 Cº)+(1 kg x 2,270,000J/kg)
= 84,000 J + 2,270,000 J = 2,354,000 J
Heat(J)
Example
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4. Ice cube has mass 100 gram at 0ºC. If it heated until 20ºC
the all ice become water. How much heat energy absorb?
(melting heat of ice = 80 cal/g ; specific heat of water 1 cal/g cº)
Known: m= 100 g
∆T = (20-0) Cº = 20 Cº
L = 80 cal/g
c = 1 cal/gCº
Question: Q total
Answer:
Q1 = m x L
Q2 = m x c x ∆T
Q total = Q 1 + Q 2
= (m x L) + (m x c x ∆T)
=(100 g x 80 cal/g ) + (100 g x 1 cal/g C ºx 20 Cº )
= 8,000 cal + 2000 cal
= 10,000 cal
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1. Calculate heat needed to change 100 gram of ice at – 30°C into
water vapor at 120°C.
cice = 2100 J/kg°C
cwater = 4200 J/kg°C
cwater vapor = 2010 J/kg°C
Lice = 336,000 J/kg
Uwater= 2,270,000 J/kg
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• Joseph Black (16 April 1728 – 6
December 1799) was a Scottish
physician, known for his
discoveries of latent heat, specific
heat, and carbon dioxide.
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• When two substances or more are mixed, the
amount of heat released by the substance
with higher temperature is equal to the
amount of heat absorbed by the substance
with lower temperature.
•
Q
released
= Q received
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100 grams of hot water at 40°C is mixed with 200 grams of water at
10°C . What is the final temperature of this mixture?
T1
Given: m1= 100 grams
T1= 40°C
T2 = 10°C
m2 = 200 grams
∆T1 = T1 - Tf
Question: Tf (Final Temperature)
Tf
Solution
Qreleased= Q received
m1. cwater . ∆T1 = m2. cwater . ∆T2
m1. cwater . (T1 – Tf) = m2. cwater . (Tf – T2) T2
m1. (T1 – Tf) = m2. (Tf – T2)
100 g(40 – Tf) = 200 g. (Tf – 10)
4000 – 100Tf = 200 Tf – 2000
4000+2000 = 200 Tf+ 100 Tf
6000 = 300 Tf
Tf = 6000/300 = 20°C
∆T2 = Tf – T2
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1. The volume of water in glass B is half of the volume of
water in glass A. The water is then mixed in glass C. The
final temperature of the water in glass C is…
2. ½ kg of hot water at 80°C is mixed with 2 kg of cold
water. What is the temperature of cold water if the final
temperature of mixture is 24°C?
THANKS!