EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 5-2 Solids, Liquids and Gases Edexcel IGCSE Physics pages 169 to 177 November 7 th 2012 Content applying to Triple.

EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 5-2

Solids, Liquids and GasesEdexcel 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’

Edexcel SpecificationSection 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 moleculesunderstand the significance of Brownian motion, as supporting evidence for particle theoryunderstand that molecules in a gas have a random motion and that they exert a force and hence a pressure on the walls of the containerunderstand that there is an absolute zero of temperature which is – 273°Cdescribe the Kelvin scale of temperature and be able to convert between the Kelvin and Celsius scalesunderstand that an increase in temperature results in an increase in the speed of gas moleculesunderstand that the Kelvin temperature of the gas is proportional to the average kinetic energy of its moleculesdescribe the qualitative relationship between pressure and Kelvin temperature for a gas in a sealed containeruse 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

States of matterSubstances can exist as solids, liquids or gases.

1. SolidsIn 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.

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2. LiquidsWhen 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.

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3. GasesWhen 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.

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Property summary tableProperty Solids Liquids Gases

definite shape yes no no

can be easily compressed no no yes

relative density high high low

can flow (fluid) no yes yes

expands to fill container no no yes

fixed volume yes yes no

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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 ____________.

spaceheated

move shape

close

molecules

WORD SELECTION:

dense

compressed

space

heated

move

shape

close

molecules

dense

compressed

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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

Brownian motionIn 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.

The yellow sphere represents the pollen grain of smoke particle.

The black particles represent water or air molecules.

Observing Brownian Motion with Smoke

The significance of Brownian Motion

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.

The yellow sphere represents the pollen grain of smoke particle.

The black particles represent water or air molecules.

Gas pressure

The particle theory of a gas explains gas pressure in the following way:

1. Gas molecules in constant random motion.

2. When a molecule collides with a surface it exerts a force on the surface as it changes its direction.

3. 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.

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.

Mathematically Boyle’s law can be stated:

p1 x V1 = p2 x V2

where:

p1 = initial gas pressure

p2 = final gas pressure

V1 = initial gas volume

V2 = final gas volume

Boyle’s law questionA 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

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.

• 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

pre

ssu

re

volume1

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.

pre

ssu

re (

kPa)

volume (cm3)

50

100

150

200

250

10 20 30 40 50

Complete:

p1 / Pa V1 / cm3 p2 / Pa V2 / cm3

100 k 30 600 k 5

100 k 30 25 15

100 k 25 20 k 75

100 k 20 80

50 k 150 k 20

10 100 k 50

5

200 k

125

25 k

60

500 k

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.

constant

forcecollide molecules

Boyle’s

random

WORD SELECTION:

multiplied temperature

constant

force

collide

molecules

Boyle’s

random

multiplied

temperature

Absolute zeroAs 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 = - 273.15°C)

It is not possible to achieve this temperature. The current (2012) record lowest temperature is: – 273.149 999 999 900 °C

This kelvin scale starts from absolute zero: 0 kelvin (0 K) = - 273 °C

A change of one kelvin is the same as a change of one °CTherefore: 0 °C (melting ice) = + 273 K

100 °C (boiling water) = + 373 K

kelvin temperature = °C temperature + 273

Note: It is incorrect to write or say “degrees kelvin”

The kelvin temperature scale

Complete (use ‘273’):Situation Celsius (oC) Absolute (K)

Intergalactic space - 270 3Vostok Antarctica 1983 - 89 184Average Earth Surface 15 288

Gas flame 1500 1773Sun’s surface 5727 6000

Gas pressure and temperature

As temperature increases:

• molecules move quickly • therefore exerting a

greater force• and so producing a

greater pressureHot gas

Cold gas

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.

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Question 1The temperature of a gas is increased from - 123°C to 377 °C. What change occurs to the average kinetic energy of the gas molecules?

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initial gas temperature = -123°C = 150 K

final gas temperature = 327°C = 600 K

the kelvin temperature increases by 4 timestherefore average kinetic energy increases by 4 times

Question 2When 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.

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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 Ktherefore final temperature = 9 x 300 K= 2700 K(or 2427 °C)

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.

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Mathematically the pressure law can be stated:

p1 = p2

T1 T2

Where:

p1 = the initial pressure

p2 = the final pressure

T1 = the initial kelvin temperature

T2 = the final kelvin temperature

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Pressure law questionA 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 / 600Kp2 = (40 000 x 600) / 200Final pressure = 120 kPa

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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.

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• 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

pre

ssu

re

kelvin temperature

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Pressure against °C temperature graph

The straight line crosses the temperature axis at absolute zero

(-273°C)

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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

50 kPa 27oC 627oC

150 kPa 450 K 100 kPa

50 kPa

800 K

160 kPa

60 K

150 kPa

27°C

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.

- 273°C pressureproportional kelvin

masskinetic

WORD SELECTION:

zero

- 273°C

pressure

proportional

kelvin

mass

kinetic

zero

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Solids, Liquids and Gases Notes questions from pages 169 to 177

1. Outline how the properties of solids, liquids and gases depend on their molecular structure and molecular movement (see pages 170 & 171)

2. What is meant by ‘Brownian Motion’?3. State Boyle’s law and describe how it can be verified

experimentally.4. State and explain how the pressure exerted by a gas changes with

temperature.5. Define the kelvin temperature scale and state the kelvin

temperature of (a) 0°C, (b) 100 °C and (c) absolute zero.6. State the pressure law and describe how it can be verified

experimentally.

7. Answer the questions on pages 176 and 177.8. Verify that you can do all of the items listed in the end of chapter

checklist on page 176.

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Solids, Liquids and Gases Notes questions from pages 169 to 177

1. What is meant by ‘Brownian Motion’?2. State Boyle’s law and describe how it can be verified

experimentally.3. State and explain how the pressure exerted by a gas

changes with temperature.4. Define the kelvin temperature scale and state the kelvin

temperature of (a) 0°C, (b) 100 °C and (c) absolute zero.

5. Answer questions 2, 4 5 and 6 on pages 176 and 177.

DOUBLE SCIENCE ONLY

Online SimulationsStates 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