Jumpin’ Jack FlashIt’s a gas gas gas!

Solids, Liquids and Gases and Gas Laws

Chapter 7

Solids, liquids and Gases

At the end of this section you should be able to:

use the kinetic theory of matter to explain properties of gases, liquids and solids

describe the qualitative effect on gases of changes in pressure, volume and temperature

describe the changes in temperature, potential energy and kinetic energy when a substance undergoes phase changes

explain the factors that affect the vapour pressure of a liquid

explain the relationship between vapour pressure and boiling temperature

use the Kinetic Theory of Matter to explain• relationship between heat and

temperature• change of phase• vapour pressure and factors that

affect vapour pressure• effect on gases of changes in

pressure, temperature and volume• the characteristics of gases• predict the effect on gases of

changes in pressure, temperature and volume (qualitative only)

• explain the boiling point of a liquid.

From the 2AB ChemistryCourse Outline

Gases, liquids and solidsBehaviour of gases − kinetic theoryGas pressure, volume and temperatureVolume and amount of gasLiquids and solidsChanges in stateEvaporation, vapour pressure and boilingPure substances and mixtures

Characteristics of Gases

Try thinking of a gas

Air is a good one

Can you list some of the gases that make up air?

N2 O2 CO2 H2 Ne He Ar

From which kind of element are these all made up?

Think about the particles of a gas

What do they look like?

Are they big? Small?

Characteristics of Gases

How would you describe a gas

what it does? what it looks like? shape? behaviour? how did it get to be a gas?

What would be the best description you could give a gas?

What are some ideas we use to describe what gases do?

PressureVolumeTemperatureHow much (number of moles)

Any more?

Kinetic Theory of Gases

What do each of these words mean?

KINETIC

THEORY

of

GASES

Ideal gas - what is this?

All gases behave in generally the same manner*, so we can generalise their behaviour and devise a set of rules to predict and describe this behaviour

THE GAS LAWS

Kinetic Theory of Gases

So which gas is an ideal gas?

Well… none of them are

Why?

Recall “All gases behave in generally the same manner*...” this is generally true for a limited set of circumstances - for a limited set of values for…

PRESSURE

VOLUME

TEMPERATURE

NUMBER OF MOLES

Kinetic Theory of Gases

Model of Gas motion

What causes the pressure of a gas in a closed container?

Impacts of gas molecules with the walls of the container.

Anything that increases the number of impacts per second or the force of each impact increases the pressure.

Microscopic View

Light molecules move faster and hit the walls more often.

Heavy molecules hit the walls with lower velocity and less frequency, but the same force.

These 2 effects exactly balance out.

**Gas pressure doesn’t depend on the identity of the gas.**

1. Gases consist of tiny particles called

molecules, except for the noble gases which

consist of atoms

Kinetic Theory of Gases

The kinetic theory of gases is the best approximation of the way gases behave.

Its description of gases is based on the following assumptions

2. The average distance between the

molecules of a gas is large compared with the size of each gas

molecule

3. The molecules of a gas move in rapid,

random, straight line motion. These

movements result in collisions with each other and with the

sides of the container

4. The molecules of a gas exert negligible

attractive or repulsive forces on one another

5. All collisions of gas molecules are

perfectly elastic. This means there is no net

energy loss during these collisions

6. The kinetic energy of the molecules increases with temperature

1. GASES R TINY

2. Little gas, lotsa space

3. Random, rapid, straight collisions

4. No attraction / repulsion

5. Collisions elastic

6. T KE

Pressure Depends on

1) the concentration or # of gas molecules per unit volume

and2) the temperature.

How fast do the molecules in the air move?

Depends on the mass. Light molecules are faster than

heavy molecules at the same temperature.

Temperature = measure of the ave. translational K.E. of the particles of a system.

Molecular Speeds at 298 K

H2 1.93 X 105 cm/sec

He 1.36 X 105 cm/sec O2 4.82 X 104

cm/sec Ar 4.31 X 104

cm/sec Xe 2.38 X 104 cm/sec

HOW ISKINETIC ENERGY DISTRIBUTED

IN A LIQUID?

LOWkineticenergy

HIGHkineticenergy

LOWkineticenergy

HIGHkineticenergy

LOWkineticenergy

HIGHkineticenergy

LOWkineticenergy

HIGHkineticenergy

LOWkineticenergy

HIGHkineticenergy

LOWkineticenergy

HIGHkineticenergy

LOWkineticenergy

HIGHkineticenergy

LOWkineticenergy

HIGHkineticenergy

HOTCOLD

LOW INTERMEDIATE HIGHkinetic kinetic kineticenergy energy energy

COLD HOT

How many water moleculeshave intermediate K.E.?

LOW INTERMEDIATE HIGHkinetic kinetic kineticenergy energy energy

COLD HOT

How many water moleculeshave HIGH K.E.?How many water moleculeshave LOW K.E.?

HOTCOLD

L O Wk in e t ice n e r g y

H IG Hk in e t ice n e r g y

INTERMEDIATEk in e t ice n e r g y

Nu

mb

er

of

part

icle

s

Nu

mb

er

of

part

icle

s

kinetic energylow high

DIS T R IB U T IO N O F K IN E T IC E N E R G Y IN A L IQ U ID

lowK.E.

highK.E.

DIS T R IB U T IO N O F K IN E T IC E N E R G Y IN A L IQ U ID

average K.E.

= temperature of liquid

Nu

mb

er

of

part

icle

s

WHAT HAPPENSTO A LIQUID’S TEMPERATURE

DURING EVAPORATION?

temperatureof liquid

lowtemperature

hightemperature

low hightemperature 1

low hightemperature2

low hightemperature2

Molecular Speed vs. Temperature

Pressure – Microscopic View

Gas molecules hit the walls of their container.

Pressure depends on Number of impacts per unit time

Force of each impact

Pressure – Macroscopic View

Pressure depends on how many gas molecules per unit volume and on the temperature.

The same amount of gas exerts different pressure at different temperatures (tires).

http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter09/Text_Images/FG09_09.JPG

Avogadro’s Law Equal volumes of gases at the same pressure and temperature

contain the same number of “particles.”

V = an where V = volume of the gas, n= # of moles of gas, & a is a constant.

3 containers – same size, same temperature, same pressure.

Box A He

Box BN2

Box C CH4

What can you say about the number of molecules in each box? It’s the same.

B = 2 X AC = 5 X A

What can you say about the number of atoms in each box?

Boyle’s Law

Boyle’s Law - words

The volume of a sample of gas is inversely proportional to its pressure, at constant temperature.

Scientists plot data because a picture shows relationships better than lists of numbers.There are lots of

“pictures” that scientists & mathematicians recognize.

http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter09/Text_Images/FG09_06.JPG

Boyle’s Law - mathematically

P X V = K, a constant

V = K/P or P = K/V

P1V1 = P2V2

For every point on the hyperbola, P X V = the same constant, K

PV vs. P

Pressure (atm)

PV

22.25-

22.30-

22.35-

22.40-

22.45-

0 0.50 1.00

- - -

--------------------------------------------------------

CO2

Ne

O2Ideal

Boyle’s Law Problems

The plunger of a bicycle pump is pushed in so that the pressure of the trapped air changes from 1.65 atm to 2.50 atm. No air can escape. Temperature is constant. The initial volume of air is 0.175 L. Calculate the final volume.

Graph the following data set and comment on whether it follows Boyle’s Law behaviour

Charles’ Law The volume of a gas at constant

pressure varies directly with its absolute temperature.

Linear Relationship

Plot Volume vs. C and you get a straight line.

The relationship between Volume and C is linear. The equation of a line is: Y = mX + b.

Charles extrapolated the graph to 0 volume.At 0 mL, the X-intercept is -273.15 C.

Hints of Kelvin scale Charles extrapolated his data to see the temperature at

which the volume was 0.

1st indication that the temperature -273 C might have a fundamental meaning.

Why did Charles have to extrapolate his lines in this temperature range instead of taking data?

Charles’ Law: Graphically

Plot Volume vs. Kelvin Temperature

Straight line that passes through the origin.

V = kT or V = k or V1/T1 = V2/T2

T

Vol

ume

Temperature

He

CH4

H2O

H2

N2O

-273.15C

Charles’ Law

A sample of a gas at 125C and 1 atm pressure occupies a volume of 55.8 liters. What volume will the it occupy at -45C?

Gas laws summary

Behaviour of Real Gases

Under pressure

Investigate the effect

on thisP1 V1 T1 n1 P2 V2 T2 n2 Do this1 22.4 273.15 1 #DIV/ 0! Double volume, keep T and n constant1 22.4 273.15 1 #DIV/ 0! Half volume, keep T and n constant1 22.4 273.15 1 #DIV/ 0! Double T, keep V and n constant1 22.4 273.15 1 #DIV/ 0! Half T, keep V and n1 22.4 273.15 1 #DIV/ 0! Double n, keep V and T constant1 22.4 273.15 1 #DIV/ 0! Half n, keep V and T constant

Investigate the effect

on thisP1 V1 T1 n1 P2 V2 T2 n2 Do this1 22.4 273.15 1 #DIV/ 0! Double P, keep V and n constant1 22.4 273.15 1 #DIV/ 0! Half P, keep V and n constant1 22.4 273.15 1 #DIV/ 0! Double V, keep P and n constant1 22.4 273.15 1 #DIV/ 0! Half V, keep P and n constant1 22.4 273.15 1 #DIV/ 0! Double n, keep V and P constant1 22.4 273.15 1 #DIV/ 0! Half n, keep V and P constant

Investigate the effect

on thisP1 V1 T1 n1 P2 V2 T2 n2 Do this1 22.4 273.15 1 #DIV/ 0! Double P, keep T and n contant1 22.4 273.15 1 #DIV/ 0! Half P, keep T and n constant1 22.4 273.15 1 #DIV/ 0! Double T, keep P and n constant1 22.4 273.15 1 #DIV/ 0! Half T, keep, P and n constant1 22.4 273.15 1 #DIV/ 0! Double n, keep P and T constant1 22.4 273.15 1 #DIV/ 0! Half n, keep P and T constant

Double click on on the spreadsheet and play around with the numbers to investigate the effect of changing different gas law parameters