1. EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 5-2 Solids, Liquids and Gases
Edexcel IGCSE Physics pages 169 to 177
November 7th 2012
Content applying to Triple Science only is shown in red type on the next slide and is indicated on subsequent slides by ‘TRIPLE ONLY’

2. Edexcel Specification
Section 5: Solids, liquids and gases
c) Change of state
understand the changes that occur when a solid melts to form a liquid, and when a liquid evaporates or boils to form a gas
describe the arrangement and motion of particles in solids, liquids and gases
d) Ideal gas molecules
understand the significance of Brownian motion, as supporting evidence for particle theory
understand that molecules in a gas have a random motion and that they exert a force and hence a pressure on the walls of the container
understand that there is an absolute zero of temperature which is – 273°C
describe the Kelvin scale of temperature and be able to convert between the Kelvin and Celsius scales
understand that an increase in temperature results in an increase in the speed of gas molecules
understand that the Kelvin temperature of the gas is proportional to the average kinetic energy of its molecules
describe the qualitative relationship between pressure and Kelvin temperature for a gas in a sealed container
use the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume:
p1 / T1 = p2 / T2
use the relationship between the pressure and volume of a fixed mass of gas at constant temperature:
p1V1 = p2V2
Red type: Triple Science Only

3. States of matter 1. Solids
TRIPLE ONLY
States of matter
Substances can exist as solids, liquids or gases.
1. Solids
In a solid the particles (molecules) vibrate about fixed positions within a close packed regular structure.
The particles cannot move in between each other which results in a solid having a definite shape and fixed volume. 3

4. 2. Liquids When a solid is heated it may melt to form a liquid.
TRIPLE ONLY
2. Liquids
When a solid is heated it may melt to form a liquid.
In a liquid the particles (molecules) move in-between each other and are approximately the same distance apart as in a solid.
A liquid does not have a definite shape but it does have a fixed volume. 4 4

5. 3. Gases When a gas is heated it may evaporate or boil to form a gas.
TRIPLE ONLY
3. Gases
When a gas is heated it may evaporate or boil to form a gas.
In a gas the particles (molecules) move in-between each other and are much further apart than they are in a liquid.
A gas takes up the shape and volume of its container. 5 5

6. Property summary table
TRIPLE ONLY
Property summary table
Property
Solids
Liquids
Gases
definite shape
yes no
can be easily compressed
relative density
high
low
can flow (fluid)
expands to fill container
fixed volume 6 6

7. TRIPLE ONLY

8. Choose appropriate words to fill in the gaps below:
TRIPLE ONLY
Choose appropriate words to fill in the gaps below:
A solid has a definite _______ due to it consisting of closely packed _________ which cannot move in-between each other.
When a solid is ________ to become a liquid the molecules can _______ in-between each other. However, the molecules remain ______ together and so a liquid is as _______ and incompressible as a solid.
When a liquid becomes a gas the molecules fill up the _____ available. A gas is therefore is easily ____________.
shape
molecules
heated
move
close
dense
space
compressed
WORD SELECTION:
molecules
dense
move
shape
heated
close
space
compressed 8 8 8

9. Molecular movement in gases
A gas consists of molecules moving about in random motion.
Due to collisions, the speed and direction of each molecule is continually changing in an unpredictable way.
random motion 9 9

10. Brownian motion
The yellow sphere represents the pollen grain of smoke particle.
The black particles represent water or air molecules.
In 1827, Robert Brown observed through a microscope the motion of pollen grains suspended in water.
The grains were seen to jerk about randomly.
A similar observation can be seen with smoke particles suspended in air.

11. Observing Brownian Motion with Smoke11 11

12. The significance of Brownian Motion
The yellow sphere represents the pollen grain of smoke particle.
The black particles represent water or air molecules.
Einstein, in 1905, proved mathematically that the motion of the smaller, invisible air molecules must be as random as the larger, visible smoke particles.
The smoke particles move much more slowly than the air molecules due to their much greater mass. 12 12

13. Gas pressure
The particle theory of a gas explains gas pressure in the following way:
Gas molecules in constant random motion.
When a molecule collides with a surface it exerts a force on the surface as it changes its direction.
The pressure exerted by the gas is equal to the total force in exerted by the molecules over an area of the surface divided by the area. 13

14. Boyle’s law
Boyle’s law states that the pressure of a gas is inversely proportional to its volume.
This means that if the volume of a gas is doubled its pressure will halve.
Boyle’s law only applies for a gas if its mass and temperature is kept constant while the volume is being changed. 14 14

15. p1 x V1 = p2 x V2 Mathematically Boyle’s law can be stated: where:
p1 = initial gas pressure
p2 = final gas pressure
V1 = initial gas volume
V2 = final gas volume 15 15

16. Boyle’s law question Boyle’s law: p1 x V1 = p2 x V2
A gas has an initial volume of 30 m3 at atmospheric pressure (100 kPa).
Calculate the final pressure of this gas if its volume is decreased to 10 m3.
Boyle’s law: p1 x V1 = p2 x V2
100 kPa x 30 m3 = p2 x 10 m3
3 000k = 10 p2
p2 = 3 000k / 10
Final pressure = 300 kPa 16

17. Checking Boyle’s law experimentally
Record the initial volume and pressure of the gas in the tube.
Use the foot pump to decrease the volume of the gas in the tube.
Record the new volume and pressure.
Use the foot pump to obtain further sets of volume and pressure measurements. 17

18. Plot a graph of pressure, p
(y-axis) against one divided by volume, 1 / V (x-axis).
If this graph is a straight line through the origin then Boyle’s law is confirmed.
Boyle’s law is also confirmed if each set of volume and pressure measurements give the same answer when they are multiplied together.
That is: p x V = a constant
pressure
volume 1 18 18

19. Pressure against volume graph
If a pressure is plotted against volume graph is plotted then a curved line is produced.
This line does not intercept either of the axes.
pressure (kPa)
volume (cm3) 50
100
150
200
250 10 20 30 40 19 19

20. Complete: p1 / Pa V1 / cm3 p2 / Pa V2 / cm3 100 k 30 600 k 5 25 1575 20 80
50 k
150 k 10 50 5
200 k
125
25 k 60
500 k 20 20

21. Choose appropriate words to fill in the gaps below:
A gas consists of particles called __________ that are in continual _________ motion.
The pressure of a gas is caused by the _______ exerted by the molecules when they ________ and rebound off the surface experiencing the pressure.
According to ________ law the pressure of a gas __________ by its volume is equal to a _________ number provided the _____________ of the gas does not change.
molecules
random
force
collide
Boyle’s
multiplied
constant
temperature
WORD SELECTION:
multiplied
temperature
constant
Boyle’s
collide
random
force
molecules 21 21 21

22. Absolute zero
As temperature decreases the average speed at which molecules move decreases.
Eventually at a temperature called absolute zero all molecules will cease moving.
Absolute zero = - 273°C
(more exactly = °C)
It is not possible to achieve this temperature.
The current (2012) record lowest temperature is:
– °C 22

23. The kelvin temperature scale
This kelvin scale starts from absolute zero:
0 kelvin (0 K) = °C
A change of one kelvin is the same as
a change of one °C
Therefore: 0 °C (melting ice) = K
100 °C (boiling water) = K
kelvin temperature = °C temperature + 273
Note: It is incorrect to write or say “degrees kelvin” 23

24. Complete (use ‘273’): Situation Celsius (oC) Absolute (K) - 270 3 - 89
Intergalactic space
- 270 3
Vostok Antarctica 1983
- 89
184
Average Earth Surface 15
288
Gas flame
1500
1773
Sun’s surface
5727
6000 24

25. Gas pressure and temperature
Cold gas
As temperature increases:
molecules move quickly
therefore exerting a greater force
and so producing a greater pressure
Hot gas 25 25

26. Molecular kinetic energy
TRIPLE ONLY
Molecular kinetic energy
As temperature increases the average speed and kinetic energy of the molecules increases.
With an ideal gas:
The average kinetic energy of the molecules is proportional to the kelvin temperature. 26

27. Question 1 The temperature of a gas is increased from
TRIPLE ONLY
Question 1
The temperature of a gas is increased from
- 123°C to 377 °C. What change occurs to the average kinetic energy of the gas molecules?
initial gas temperature
= -123°C
= 150 K
final gas temperature
= 327°C
= 600 K
the kelvin temperature increases by 4 times
therefore average kinetic energy increases by 4 times 27

28. TRIPLE ONLY
Question 2
When the temperature of a gas is increased from 27°C the average speed of the molecules increases three fold. Calculate the final temperature of the gas.
kinetic energy = ½ mv2
If the speed, v increases by 3 times, the kinetic energy increases by 32, 9 times.
and so the kelvin temperature increases by 9 times.
initial temperature = 27°C
= 300 K
therefore final temperature = 9 x 300 K
= 2700 K
(or 2427 °C) 28

29. TRIPLE ONLY
The Pressure Law
The pressure law states that the pressure of a fixed mass of gas at a constant volume is proportional to its kelvin temperature.
This means that if the kelvin temperature of a gas is doubled its pressure will also double. 29

30. p1 = p2 T1 T2 Mathematically the pressure law can be stated: Where:
TRIPLE ONLY
Mathematically the pressure law can be stated:
p1 = p2
T T2
Where:
p1 = the initial pressure
p2 = the final pressure
T1 = the initial kelvin temperature
T2 = the final kelvin temperature 30 30

31. TRIPLE ONLY
Pressure law question
A gas has an initial pressure of 40kPa at a temperature of - 73oC. Calculate the final pressure of this gas if its temperature is increased to 327oC at a constant volume.
Pressure law: p1 / T1 = p2 / T2
Temperatures must be in kelvin!
so: T1 = 200K and T2 = 600K
40 kPa / 200K = p2 / 600K
p2 = ( x 600) / 200
Final pressure = 120 kPa 31

32. Checking the pressure law experimentally
TRIPLE ONLY
Checking the pressure law experimentally
Record the initial pressure of the air in the round bottomed flask and the temperature of the water bath which is equal to the temperature of the air.
Use the heater to increase the temperature.
Record the new temperature and pressure.
Obtain further sets of temperature and pressure measurements.
Convert all temperature measurements to kelvin. 32 32

33. Plot a graph of pressure, p
TRIPLE ONLY
Plot a graph of pressure, p
(y-axis) against temperature in kelvin, T (x-axis).
If this graph is a straight line through the origin then the pressure law is confirmed.
The pressure law is also confirmed if each set of kelvin temperature and pressure measurements give the same answer when the pressure is divided by the kelvin temperature.
That is: p ÷ V = a constant
pressure
kelvin temperature 33 33

34. Pressure against °C temperature graph
TRIPLE ONLY
Pressure against °C temperature graph
The straight line crosses the temperature axis at absolute zero
(-273°C) 34 34

35. Complete: p1 T1 p2 T2 100 kPa 300 K 150 K 60 kPa 200 K 240 kPa 800 K
TRIPLE ONLY
Complete: p1 T1 p2 T2
100 kPa
300 K
150 K
60 kPa
200 K
240 kPa
800 K
120 kPa
600 K
50 kPa
300 kPa
360 K
27oC
627oC
150 kPa
450 K
50 kPa
800 K
160 kPa
60 K
150 kPa
27°C 35

36. Choose appropriate words to fill in the gaps below:
TRIPLE ONLY
Choose appropriate words to fill in the gaps below:
When the _______ temperature of a gas is doubled the average _______ energy of its molecules is also doubled.
The ________ law states that the pressure of a gas is ___________ to its kelvin temperature provided its ______ and volume remain constant.
According to the pressure law, the pressure of a gas should fall to _______ at a temperature of _________, also known as absolute zero.
kelvin
kinetic
pressure
proportional
mass
zero
- 273°C
WORD SELECTION:
proportional
- 273°C
pressure
kelvin
kinetic
zero
mass 36 36

37. Solids, Liquids and Gases Notes questions from pages 169 to 177
TRIPLE ONLY
Solids, Liquids and Gases Notes questions from pages 169 to 177
Outline how the properties of solids, liquids and gases depend on their molecular structure and molecular movement (see pages 170 & 171)
What is meant by ‘Brownian Motion’?
State Boyle’s law and describe how it can be verified experimentally.
State and explain how the pressure exerted by a gas changes with temperature.
Define the kelvin temperature scale and state the kelvin temperature of (a) 0°C, (b) 100 °C and (c) absolute zero.
State the pressure law and describe how it can be verified experimentally.
Answer the questions on pages 176 and 177.
Verify that you can do all of the items listed in the end of chapter checklist on page 176.

38. Solids, Liquids and Gases Notes questions from pages 169 to 177
DOUBLE SCIENCE ONLY
Solids, Liquids and Gases Notes questions from pages 169 to 177
What is meant by ‘Brownian Motion’?
State Boyle’s law and describe how it can be verified experimentally.
State and explain how the pressure exerted by a gas changes with temperature.
Define the kelvin temperature scale and state the kelvin temperature of (a) 0°C, (b) 100 °C and (c) absolute zero.
Answer questions 2, 4 5 and 6 on pages 176 and 177. 38

39. Online Simulations
States of matter - PhET - Watch different types of molecules form a solid, liquid, or gas. Add or remove heat and watch the phase change. Change the temperature or volume of a container and see a pressure-temperature diagram respond in real time. Relate the interaction potential to the forces between molecules
Gas Properties -PhET - Pump gas molecules to a box and see what happens as you change the volume, add or remove heat, change gravity, and more. Measure the temperature and pressure, and discover how the properties of the gas vary in relation to each other.
Molecular model of an ideal gas This has gas molecules in a cylinder-piston set up. Volume, pressure etc. can be varied - NTNU
Brownian Motion - NTNU
Brownian Motion - Virginia