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Jumpin’ Jack FlashIt’s a gas gas gas!
Solids, Liquids and Gases and Gas LawsChapter 7
Solids, liquids and GasesAt 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 GasesTry thinking of a gasAir is a good oneCan you list some of the gases that make up air?N2 O2 CO2 H2 Ne He ArFrom which kind of element are these all made up?
Think about the particles of a gasWhat do they look like?Are they big? Small?
Characteristics of GasesHow 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 GasesWhat do each of these words mean?KINETICTHEORYofGASES
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 GasesSo which gas is an ideal gas?Well… none of them areWhy?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…
PRESSUREVOLUME
TEMPERATURENUMBER 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 GasesThe 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 TINY2. Little gas, lotsa
space3. Random, rapid, straight
collisions4. No attraction / repulsion5. 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
HIGHkineticenergyHOTCOLD
LOW INTERMEDIATE HIGHkinetic kinetic kineticenergy energy energy
COLD HOT
How many water moleculeshave intermediate K.E.?
LOW INTERMEDIATE HIGHkinetic kinetic kineticenergy energy energyCOLD HOT
How many water moleculeshave HIGH K.E.?How many water moleculeshave LOW K.E.?
HOTCOLD
L O Wk in e tice 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
Num
ber o
f par
ticle
s
Num
ber o
f par
ticle
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
Num
ber o
f par
ticle
s
WHAT HAPPENSTO A LIQUID’S TEMPERATURE
DURING EVAPORATION?
temperatureof liquid
lowtemperature
hightemperature
low hightemperature 1
low hightemperature2
low hightemperature2
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 - mathematicallyP 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
Volu
me
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 pressureInvestigate 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