Topic 3
Thermal physics
Learn the definitions. We will be having a definitions
test next Thursday 10th December.
Homework
What is Temperature?
TemperatureTEMPERATURE determines the direction of flow of thermal energy between two bodies in thermal contact
HOT COLD
This is another way of saying that if an object is hotter than another, heat energy will flow from the hotter object to the colder!
Obvious, but important to remember!
Temperature
Temperature is also a measure of the average random kinetic energy of the particles in a substance.
Note that they are not all travelling at the same speed.
Temperature
The hotter the temperature, the faster the average speed of the particles
Note that they are not all travelling at the same speed.
Thermal equilibriumTwo bodies in thermal contact will eventually reach the same temperature. The two bodies are now said to be in thermal equilibrium.
WARM WARM
Measuring Temperature
In 1742, Andreas Celcius created the temperature scale that is known by his name.
I’ve never heard of the Andreas scale, it must be a European thing
Celcius Scale
In the Celcius scale, a value of zero degrees is assigned to the freezing point of water, and a value of one hundred degrees to the boiling point of water.
Making a Celcius thermometerPlace a glass tube containing mercury in a mixture of ice and water and labelling the position of the mercury as zero.
0°C
Making a Celcius thermometerThen place the tube in boiling water and label the new length as 100°C.
0°C
100°C
Making a Celcius thermometerFinally the range from 0 to 100 is subdivided into equal intervals.
0°C
100°C
Kelvin Temperature
• Lord Kelvin
• 1824-1907
Pressure and Temperature
• http://phet.colorado.edu/sims/ideal-gas/gas-properties_en.jnlp
Kelvin Temperature
Kelvin temperature is proportional to the average random kinetic energy of the particles in a substance.
Note that they are not all travelling at the same speed.
Absolute/Kelvin temperature and Celsius
T (in Kelvin) = T (in degrees Celcius) + 273
Just to mention for now that zero Kelvin is the lowest possible temperature.
Measuring temperature
The thermometer has to be placed in thermal contact with whatever is being measured until the thermometer and object are in thermal equilibrium.
0°C
100°
CWe’ll measure
some temperatures in a moment
So what is heat?
So what is heat?
Heat is the amount of thermal energy. For example, the sparks from a sparkler are at around 800°C but do not burn your skin. However, a hot cup of tea at around 100°C will burn your hand badly. This is because the tea contains more heat energy, even though it is cooler.
Internal Energy
This is the sum of the kinetic energies and potential energies of the particles in a substance
If you imagine the forces between particles as a spring, you can see if the particles are pulled apart or squashed together that energy is stored in the spring. Similarly there is potential energy between the particles in a substance.
Internal Energy
The internal energy of a substance can be changed by heating it (or taking heat from it) or by doing work on the object (or having the object do work).
Heat transfer
Conduction, convection and radiation.I’m not going to say anything about these, you should know it already. Can you construct a heat transfer
mind-map?
Who is Mr Porter?
Mr Porter
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Mr Porter
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Mr Porter
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familyplaces
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teaching
red wine
dogsbanks Mr Bean
rudenessdogs
shopping
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3 kids
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Mr Porter
likes
dislikes
familyplaces
tea
newspapers
footballKirsten Dunst
teaching
red wine
dogsbanks Mr Bean
rudenessdogs
shopping
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3 kids
wifeEngland
NorwayPNG
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USA
Mr Porter
likes
dislikes
familyplaces
tea
newspapers
footballKirsten Dunst
teaching
red wine
dogsbanks Mr Bean
rudenessdogs
shopping
music
3 kids
wifeEngland
NorwayPNG
Peru
Tetley
Milk, no sugar
Guardian
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Independent Nottingham Forest
Spiderman
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Gato negro
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USA
Mr Porter
likes
dislikes
familyplaces
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newspapers
footballKirsten Dunst
teaching
red wine
dogsbanks Mr Bean
rudenessdogs
shopping
music
3 kids
wifeEngland
NorwayPNG
Peru
Tetley
Milk, no sugar
Guardian
Times
Independent Nottingham Forest
Spiderman
trumpet
physics
Gato negro
rockclassical
Alice
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AlisonUSA
Mr Porter
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dislikes
familyplaces
tea
newspapers
footballKirsten Dunst
teaching
red wine
dogsbanks Mr Bean
rudenessdogs
shopping
music
3 kids
wifeEngland
NorwayPNG
Peru
Tetley
Milk, no sugar
Guardian
Times
Independent Nottingham Forest
Spiderman
trumpet
physics
Gato negro
rockclassical
Alice
George
Louis
Alison
clothes
Poo!queuingBlackadder
Natwest
Poo!
USA
Mr Porter
likes
dislikes
familyplaces
tea
newspapers
footballKirsten Dunst
teaching
red wine
dogsbanks Mr Bean
rudenessdogs
shopping
music
3 kids
wifeEngland
NorwayPNG
Peru
Tetley
Milk, no sugar
Guardian
Times
Independent Nottingham Forest
Spiderman
trumpet
physics
Gato negro
rockclassical
Alice
George
Louis
Alison
clothes
Poo!queuingBlackadder
NatwestPoo!
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Mr Porter
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dislikes
familyplaces
tea
newspapers
footballKirsten Dunst
teaching
red wine
dogsbanks Mr Bean
rudenessdogs
shopping
music
3 kids
wifeEngland
NorwayPNG
Peru
Tetley
Milk, no sugar
Guardian
Times
Independent Nottingham Forest
Spiderman
trumpet
physics
Gato negro
rockclassical
Alice
George
Louis
Alison
clothes
Poo!queuingBlackadder
NatwestPoo!
Oslo
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likes
dislikes
familyplaces
tea
newspapers
footballKirsten Dunst
teaching
red wine
dogsbanks Mr Bean
rudenessdogs
shopping
music
3 kids
wifeEngland
NorwayPNG
Peru
Tetley
Milk, no sugar
Guardian
Times
Independent Nottingham Forest
Spiderman
trumpet
physics
Gato negro
rockclassical
Alice
George
Louis
Alison
clothes
Poo!queuingBlackadder
NatwestPoo!
Oslo
Port Moresby
Lima
Twice European Champions Wimbledon
CD
Bristol University
cheap
Rush
Bruckner
14
12
11
21
Marks and Spencer
Norway!Lik lik hus
Heat transfer
Conduction, convection and radiation.
I’m not going to say anything about these, you should know it already. Can you construct a heat transfer
mind-map?
ColoursFew words
ConnectionsDrawings
Measuring temperature practical
Moles!
Hi Chris!
Moles!
Equal masses of different elements will contain different numbers of atoms (as atoms of different elements have different masses)
Moles!
It is sometimes useful for physicists and chemists (but we don’t care about them) to compare the number of atoms or molecules in an amount of substance.
To do this we use the idea of moles.
A chemist
Moles!
• One mole of a substance contains the same number of molecules/atoms as in 12 grams of carbon-12.
• This number (of atoms or molecules) is known as the Avogadro constant (NA) which is equal to 6.02 x 1023
You need to learn this definition.
How big is 6 x 1023?
Imagine the whole of the United states
You are here!
How big is 6 x 1023?
Imagine the whole of the United states covered in unpopped popcorn
How big is 6 x 1023?
Imagine the whole of the United states covered in unpopped popcorn to a depth of six miles!
How big is 6 x 1023?
Imagine the whole of the United states covered in unpopped popcorn to a depth of six miles! Count the grains and that is 6 x 1023!
600000000000000000000000
Moles!
For example, Hydrogen (H2) has a relative molecular mass of 2, so 2 grams of hydrogen (one mole) contains the same number of molecules as atoms in 12g of carbon-12 (6.02 x 1023)
Moles!
It follows therefore that 7g of lithium (atomic mass 7), 20g neon (atomic mass 20) or 39 g potassium (atomic mass 39) all contain the same number of atoms (1 mole or 6.02 x 1023 atoms)
Moles!
• The number of moles of a substance can thus be found by dividing the mass of substance by its relative atomic or molecular mass
n = mass/RAM
Example
How many moles of sulphur atoms are there in 80g of sulphur? How many grams of carbon would have the same number of atoms?
Example
How many moles of sulphur atoms are there in 80g of sulphur? How many grams of carbon would have the same number of atoms?
N = mass/RAM = 80/32 = 2.5 moles
Example
How many moles of sulphur atoms are there in 80g of sulphur? How many grams of carbon would have the same number of atoms?
N = mass/RAM = 80/32 = 2.5 moles
Mass of carbon = RAM x n = 12 x 2.5 = 30 g
Relative formula mass
We can use the idea of moles and apply it to molecules using relative formula mass.
C2H5OH
RFM = (2 x 12) + (6 x 1) + (1 x 16) = 46
46g of ethanol = I mole of ethanol molecules
What about moles and
gases?
Equal volumes
Luckily, equal volumes of gas contain the same number of particles (at the same temperature and pressure)
Equal volumes
For example, 1 litre of nitrogen contains the same number of molecules as there are atoms in one litre of Argon.
A litre is 1000 cm3 or 1 dm3
Mole of gas
One mole of any gas occupies 24 dm3 (24000 cm3) at standard temperature and pressure (25°C and 1 atmosphere)
You will be given this in a
question
Moles of gas = volume (cm3)/24000 = volume (dm3)/24
Learn this!
Let’s try some questions:
Pages 161 and 162Questions 1, 2, 4, 5 and 6
Don’t forget to read the relevant pages in your
textbook (Pages 158-162)