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?

Mind-map

Who is Mr Porter?

Mr Porter

Mr Porter

likes

dislikes

familyplaces

Mr Porter

likes

dislikes

familyplaces

tea

newspapers

footballKirsten Dunst

teaching

red wine

music

Mr Porter

likes

dislikes

familyplaces

tea

newspapers

footballKirsten Dunst

teaching

red wine

dogsbanks Mr Bean

rudenessdogs

shopping

music

Mr Porter

likes

dislikes

familyplaces

tea

newspapers

footballKirsten Dunst

teaching

red wine

dogsbanks Mr Bean

rudenessdogs

shopping

music

3 kids

wife

Mr Porter

likes

dislikes

familyplaces

tea

newspapers

footballKirsten Dunst

teaching

red wine

dogsbanks Mr Bean

rudenessdogs

shopping

music

3 kids

wifeEngland

NorwayPNG

Peru

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

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

AlisonUSA

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

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!

Oslo

Port Moresby

Lima

USAHouston

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!

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

USA Houston

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!

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)