1

1

GasesGases

Properties of GasesProperties of Gases

Gas PressureGas Pressure

2

GasesGases

What gases are important for each of the What gases are important for each of the following: Ofollowing: O22, CO, CO22 and/or He?and/or He?

A. B. C. D.A. B. C. D.

3

GasesGases

What gases are important for each of the What gases are important for each of the following: Ofollowing: O22, CO, CO22 and/or He?and/or He?

A. COA. CO22 B. OB. O22/CO/CO22 C. OC. O22 D. HeD. He

2

4

KineticKinetic--Molecular Theory of MatterMolecular Theory of Matter

�� Particles of Matter are always in Particles of Matter are always in motionmotion

�� Ideal GasesIdeal Gases --an imaginary gas that an imaginary gas that fits all the assumptions of the theoryfits all the assumptions of the theory

�� Kinetic Energy (KE) formulaKinetic Energy (KE) formula�� Physical properties of gasesPhysical properties of gases�� Real gasesReal gases -- gases in our daily livesgases in our daily lives

5

Ideal GasIdeal Gas--imaginary gas that fits all imaginary gas that fits all the following assumptions.the following assumptions.

Particles in gases: Particles in gases:

��Are very far apartAre very far apart

��Have collisions that are elastic (no KE loss)Have collisions that are elastic (no KE loss)

��Move rapidly Move rapidly

��Have no attraction (or repulsion) Have no attraction (or repulsion)

��Have energy increases at higher temperaturesHave energy increases at higher temperatures

6

Kinetic Energy of GasesKinetic Energy of Gases

�� At the same temperature, all gas At the same temperature, all gas particles have the same amount of particles have the same amount of energyenergy–– Lighter particles move faster than Lighter particles move faster than

heavier particlesheavier particles–– KE = KE = mvmv 22 KE =kinetic energy KE =kinetic energy

22 v = velocity (speed)v = velocity (speed)m = massm = mass

3

7

Physical Properties of GasesPhysical Properties of Gases

�� Gases are compressibleGases are compressible

�� Gases have low densitiesGases have low densities

�� Gases fill a container completely and uniformlyGases fill a container completely and uniformly��Gases exert a uniform pressure on all inner Gases exert a uniform pressure on all inner

surfaces of their containerssurfaces of their containers�� Fluidity: gas particles can slide past one another Fluidity: gas particles can slide past one another

(gases and liquids are (gases and liquids are ““fluidsfluids””))� Diffusion: gases move from high concentration to

low concentration

8

Real GasesReal Gases

�� Close to ideal gas at standard Close to ideal gas at standard conditionsconditions–– Have volume Have volume –– Attraction between particlesAttraction between particles

�� Deviation from ideal gas is greater Deviation from ideal gas is greater whenwhen–– Particles are close togetherParticles are close together

»» Low temperaturesLow temperatures»» High pressuresHigh pressures

–– Gas is a compound rather than an Gas is a compound rather than an elementelement

9

Some Gases in Our LivesSome Gases in Our Lives

Air:Air:

oxygen Ooxygen O22 nitrogen Nnitrogen N22 ozone Oozone O33

argon argon ArAr carbon dioxide COcarbon dioxide CO2 2 water Hwater H22OONoble gasesNoble gases: :

helium He neon Ne krypton Kr xenon helium He neon Ne krypton Kr xenon XeXeOther gases:Other gases:

fluorine Ffluorine F22 chlorine Clchlorine Cl22 ammonia NHammonia NH3 3

methane CHmethane CH44 carbon monoxide COcarbon monoxide CO

nitrogen dioxide NOnitrogen dioxide NO22 sulfur dioxide SOsulfur dioxide SO22

4

10

PressurePressure�� Force per unit areaForce per unit area�� P = P = forceforce

areaarea�� Gas pressure is a result of collisions Gas pressure is a result of collisions

of gas particles. Depends on:of gas particles. Depends on:–– Number of gas particlesNumber of gas particles–– Temperature Temperature –– VolumeVolume

11

Instruments used to measure pressureInstruments used to measure pressure

�� Barometer Barometer –– measures atmospheric measures atmospheric pressurepressure

�� Manometer Manometer –– measures gas pressure measures gas pressure of a containerof a container

12

BarometersBarometers

760 mmHg760 mmHg

atmatm

pressurepressure

5

13

ManometerManometer

14

Unit of Pressure Unit of Pressure

One atmosphere (1 One atmosphere (1 atmatm) )

��Is the average pressure of the Is the average pressure of the

atmosphere at sea level atmosphere at sea level

��Is the standard of pressureIs the standard of pressure

1.00atm1.00atm==760mmHg760mmHg==760torr760torr==101.3kPa101.3kPa==14.7psi14.7psi

15

Types of Pressure UnitsTypes of Pressure Units

PressurePressure Used inUsed in

760 mm Hg or 760 760 mm Hg or 760 torrtorr ChemistryChemistry

14.7 lb/in.14.7 lb/in.22 U.S. pressure gaugesU.S. pressure gauges

29.9 in. Hg29.9 in. Hg U.S. weather reportsU.S. weather reports

101.3 101.3 kPakPa (kilopascals)(kilopascals) Weather in all Weather in all countries except U.S.countries except U.S.

1.013 bars1.013 bars Physics and Physics and astronomyastronomy

6

16

ConversionsConversions�� 760.mmHg760.mmHg ==760.torr760.torr ==1.00atm1.00atm==101.3kPa101.3kPa==14.7psi14.7psiWhat is 2.00 What is 2.00 atmatm expressed in expressed in torrtorr

17

ConversionsConversions�� 760.mmHg760.mmHg ==760.torr760.torr ==1.00atm1.00atm==101.3kPa101.3kPa==14.7psi14.7psiWhat is 2.00 What is 2.00 atmatm expressed in expressed in torrtorr

2.00atm

1 1.00atm760.torr

= 1520torr

18

ConversionsConversions�� 760.mmHg760.mmHg ==760.torr760.torr ==1.00atm1.00atm==101.3kPa101.3kPa==14.7psi14.7psi

�� The pressure of a tire is measured The pressure of a tire is measured as 32.0 psi.as 32.0 psi.

What is this pressure in What is this pressure in kPakPa??

7

19

ConversionsConversions�� 760.mmHg760.mmHg ==760.torr760.torr ==1.00atm1.00atm==101.3kPa101.3kPa==14.7psi14.7psi

�� The pressure of a tire is measured The pressure of a tire is measured as 32.0 psi.as 32.0 psi.

What is this pressure in What is this pressure in kPakPa??

32.0psi1

101.3kPa14.7psi = 221kPa

20

Gas LawsGas Laws

�� BoyleBoyle ’’s Laws Law�� CharlesCharles ’’ LawLaw�� GayGay--LussacLussac ’’s Laws Law�� Combined Gas LawCombined Gas Law

21

BoyleBoyle’’ s Laws Law

�� Reducing the volume by oneReducing the volume by one --half half doubles the pressuredoubles the pressure

�� The volume of a fixed mass of gas The volume of a fixed mass of gas varies inversely with the pressure at varies inversely with the pressure at constant temperatureconstant temperature

�� PP11VV11 –– PP22VV22

8

22

As the pressure As the pressure As the pressure As the pressure increasesincreasesincreasesincreases

As the pressure As the pressure As the pressure As the pressure increasesincreasesincreasesincreases

VolumeVolumeVolumeVolumedecreasesdecreasesdecreasesdecreases

VolumeVolumeVolumeVolumedecreasesdecreasesdecreasesdecreases

23

How does Pressure and Volume of gases relate graphically?

How does Pressure and Volume of gases relate graphically?

Volume

Volume

PressurePressure

PV = kPV = k

Temperature, Temperature, Temperature, Temperature, # of particles# of particles# of particles# of particlesremain constantremain constantremain constantremain constant

Temperature, Temperature, Temperature, Temperature, # of particles# of particles# of particles# of particlesremain constantremain constantremain constantremain constant

24

BoyleBoyle’’s Mathematical Laws Mathematical LawP1V1 = P2V2P1V1 = P2V2

EXAMPLE:A gas has a volume of 3.0 L at 2.0 atm.

What is its volume at 4.0 atm?

9

25

1.Determine which variables you have:

� What variable does the unit “atm” go with?� P1 =

� P2=� What variable does the unit “L” go with?

� V1=� V2=

26

2. Determine which law is being 2. Determine which law is being represented.represented.

�� Which law deals with only Pressure Which law deals with only Pressure and volume?and volume?

�� BoyleBoyle ’’s Laws Law

27

3. Write the formula and Plug in 3. Write the formula and Plug in numbers and unitsnumbers and units

�� PP11VV11 = P= P22 VV22

�� (2.0atm)(3.0mL) = (4.0atm)(V(2.0atm)(3.0mL) = (4.0atm)(V 22))

10

28

4. Get the unknown variable alone4. Get the unknown variable alone

�� (2.0atm)(3.0mL) (2.0atm)(3.0mL) = V= V22

4.0atm4.0atm

29

5. Plug in your calculator and solve5. Plug in your calculator and solve

�� VV22 = 1.5L= 1.5L

30

Learning Check Learning Check

A sample of nitrogen gas is 6.4 L at a pressure A sample of nitrogen gas is 6.4 L at a pressure of 0.70 atm. What will the new volume be if of 0.70 atm. What will the new volume be if the pressure is changed to 1.40 the pressure is changed to 1.40 atmatm? (T ? (T constant) Explain.constant) Explain.

1) 3.2 L1) 3.2 L

2) 6.4 L2) 6.4 L

3) 12.8 L3) 12.8 L

11

31

SolutionSolution

A sample of nitrogen gas is 6.4 L at a pressure A sample of nitrogen gas is 6.4 L at a pressure of 0.70 atm. What will the new volume be if of 0.70 atm. What will the new volume be if the pressure is changed to 1.40 the pressure is changed to 1.40 atmatm? (T ? (T constant)constant)

6.4 L x 6.4 L x 0.70 0.70 atmatm = = 3.2 L (1)3.2 L (1)

1.40 1.40 atmatm

Volume must decrease to cause an increase Volume must decrease to cause an increase in the pressurein the pressure

32

Learning CheckLearning Check

A sample of helium gas has a volume of A sample of helium gas has a volume of 12.0 L at 600. mm Hg. What new pressure 12.0 L at 600. mm Hg. What new pressure is needed to change the volume to 36.0 L? is needed to change the volume to 36.0 L? (T constant) Explain.(T constant) Explain.

1) 200. mmHg 1) 200. mmHg

2) 400. mmHg 2) 400. mmHg

3) 1200 mmHg3) 1200 mmHg

33

SolutionSolution

A sample of helium gas has a volume of A sample of helium gas has a volume of 12.0 L at 600. mm Hg. What new pressure 12.0 L at 600. mm Hg. What new pressure is needed to change the volume to 36.0 L? is needed to change the volume to 36.0 L? (T constant) Explain.(T constant) Explain.

600. mm Hg x 600. mm Hg x 12.0 L12.0 L = 200. mmHg (1) = 200. mmHg (1)

36.0 L36.0 L

Pressure decrease when volume increases.Pressure decrease when volume increases.

12

34

Volume of balloon Volume of balloon Volume of balloon Volume of balloon at room at room at room at room

temperaturetemperaturetemperaturetemperature

Volume of balloon Volume of balloon Volume of balloon Volume of balloon at room at room at room at room

temperaturetemperaturetemperaturetemperature

Volume of balloon Volume of balloon Volume of balloon Volume of balloon at 5at 5at 5at 5°°°°CCCC

Volume of balloon Volume of balloon Volume of balloon Volume of balloon at 5at 5at 5at 5°°°°CCCC

35

CharlesCharles’’ Law: V and TLaw: V and T

At constant pressure, the volume of a gas isAt constant pressure, the volume of a gas is

directly related to its absolute (K) temperaturedirectly related to its absolute (K) temperature

VV11 = = VV22 oror VV11TT22 = V= V22TT11

TT11 TT22

K = K = °°C + 273C + 273

36 Temp

How does Temperature and How does Temperature and How does Temperature and How does Temperature and Volume of gases relate graphically?Volume of gases relate graphically?Volume of gases relate graphically?Volume of gases relate graphically?

How does Temperature and How does Temperature and How does Temperature and How does Temperature and Volume of gases relate graphically?Volume of gases relate graphically?Volume of gases relate graphically?Volume of gases relate graphically?

Volume

Pressure, Pressure, Pressure, Pressure, # of particles# of particles# of particles# of particlesremain constantremain constantremain constantremain constant

Pressure, Pressure, Pressure, Pressure, # of particles# of particles# of particles# of particlesremain constantremain constantremain constantremain constant

13

37

Learning CheckLearning Check

Use CharlesUse Charles’’ Law to complete the statements Law to complete the statements

below:below:

1. If final T is higher than initial T, final V1. If final T is higher than initial T, final V

is (is (greater, or lessgreater, or less) than the initial V.) than the initial V.

2. If final V is less than initial V, final T is2. If final V is less than initial V, final T is

((higher, or lowerhigher, or lower) than the initial T.) than the initial T.

38

Solution GL3Solution GL3

1. If final T is higher than initial T, final V1. If final T is higher than initial T, final V

is (is (greatergreater) than the initial V.) than the initial V.

2. If final V is less than initial V, final T is (2. If final V is less than initial V, final T is (lowerlower) ) than the initial T.than the initial T.

39

Learning Check Learning Check

A sample of oxygen gas has a volume of A sample of oxygen gas has a volume of 420 mL at a temperature of 18420 mL at a temperature of 18°°C. What C. What temperature (in temperature (in °°C) is needed to change C) is needed to change the volume to 640 mL?the volume to 640 mL?

1) 4431) 443°°CC 2) 1702) 170°°C 3) C 3) -- 8282°°CC

14

40

Solution Solution

A sample of oxygen gas has a volume of A sample of oxygen gas has a volume of 420 mL at a temperature of 18420 mL at a temperature of 18°°C. What C. What temperature (in temperature (in °°C) is needed to change C) is needed to change the volume to 640 mL?the volume to 640 mL?2) 170°C

T2 =(291K)(640mL)=443 K

420 mL

T2 =443 K - 273 K = 170°C

41

GayGay--LussacLussac’’ s Law: P and Ts Law: P and T

Doubling the Kelvin temperature doubles the pressure

The pressure of a fixed mass of gas at constant volume varies directly with the Kelvin temperature

P1 = P2 or P1T2 = P2T1T1 T2

42

Pressure Pressure Pressure Pressure GaugeGaugeGaugeGauge

Pressure Pressure Pressure Pressure GaugeGaugeGaugeGauge

Car before a tripCar before a tripCar before a tripCar before a tripCar before a tripCar before a tripCar before a tripCar before a trip

Think of a tire...Think of a tire...Think of a tire...Think of a tire...Think of a tire...Think of a tire...Think of a tire...Think of a tire...

LetLetLetLet’’’’s get ons get ons get ons get onthe road the road the road the road Dude!Dude!Dude!Dude!

15

43

Car after a long tripCar after a long tripCar after a long tripCar after a long tripCar after a long tripCar after a long tripCar after a long tripCar after a long trip

Think of a tire...Think of a tire...Think of a tire...Think of a tire...Think of a tire...Think of a tire...Think of a tire...Think of a tire...

WHEW!WHEW!WHEW!WHEW!

Pressure Pressure Pressure Pressure GaugeGaugeGaugeGauge

Pressure Pressure Pressure Pressure GaugeGaugeGaugeGauge

44 Temp

Pressure

How does Pressure and How does Pressure and How does Pressure and How does Pressure and Temperature of gases relate Temperature of gases relate Temperature of gases relate Temperature of gases relate

graphically?graphically?graphically?graphically?

How does Pressure and How does Pressure and How does Pressure and How does Pressure and Temperature of gases relate Temperature of gases relate Temperature of gases relate Temperature of gases relate

graphically?graphically?graphically?graphically?

Volume, Volume, Volume, Volume, # of particles# of particles# of particles# of particlesremain constantremain constantremain constantremain constant

Volume, Volume, Volume, Volume, # of particles# of particles# of particles# of particlesremain constantremain constantremain constantremain constant

45

PT ProblemPT Problem

A gas has a pressure at 2.0 A gas has a pressure at 2.0 atmatm at 18at 18°°C. C. What will be the new pressure if the What will be the new pressure if the temperature rises to 62temperature rises to 62°°C? (V constant)C? (V constant)

T = 18T = 18°°C T = 62C T = 62°°CC

16

46

PT CalculationPT Calculation

PP11 = 2.0 = 2.0 atmatm TT11 = 18= 18°°C + 273 = 291 KC + 273 = 291 K

PP22 = ?= ? TT22 = 62= 62°°C + 273 = 335 KC + 273 = 335 K

PP22 = (P= (P11 )()(TT22))

TT11

PP22 = (2.0 atm)(= (2.0 atm)(335K)335K) = = atmatm

291K291K

PP2 2 = 2.3 = 2.3 atmatm

?

47

Learning Check Learning Check

Use GayUse Gay--LussacLussac’’s law to complete the statements s law to complete the statements below: below:

1. When temperature decreases, the1. When temperature decreases, the

pressure of a gas (pressure of a gas (decreases or increasesdecreases or increases).).

2. When temperature increases, the pressure 2. When temperature increases, the pressure

of a gas of a gas (decreases or increases(decreases or increases).).

48

Solution Solution

1. When temperature decreases, the1. When temperature decreases, the

pressure of a gas (pressure of a gas (decreasesdecreases).).

2. When temperature increases, the2. When temperature increases, the

pressure of a gas (pressure of a gas (increasesincreases).).

17

49V, nV, nPP11/T/T11 = P= P22/T/T22PP↑↑↑↑↑↑↑↑ TT↑↑↑↑↑↑↑↑GayGay--LussacLussac ’’ss

P, nP, nVV11/T/T11 = V= V22/T/T22VV↑↑↑↑↑↑↑↑ TT↑↑↑↑↑↑↑↑CharlesCharles ’’

T, nT, nPP11VV1 1 = P= P22VV22PP↑↑↑↑↑↑↑↑ VV↓↓↓↓↓↓↓↓BoyleBoyle ’’ss

CONCON--STANTSTANTLAWLAWRELATRELAT--IONSHIPIONSHIPLAWLAW

50

Learning Check Learning Check

Complete with Complete with 1) Increases 2) Decreases 1) Increases 2) Decreases

3) Does not change3) Does not change

A. Pressure _____, when V decreasesA. Pressure _____, when V decreases

B. When T decreases, V _____.B. When T decreases, V _____.

C. Pressure _____ when V changes from 12.0 L to C. Pressure _____ when V changes from 12.0 L to 24.0 L (constant n and T)24.0 L (constant n and T)

D. Volume _____when T changes from 15.0 D. Volume _____when T changes from 15.0 °°C to C to 45.045.0°°C (constant P and n)C (constant P and n)

51

Solution Solution

A. Pressure A. Pressure 1) Increases1) Increases, when V decreases, when V decreases

B. When T decreases, V B. When T decreases, V 2) Decreases2) Decreases

C. Pressure C. Pressure 2) Decreases 2) Decreases when V changes when V changes

from 12.0 L to 24.0 L (constant n and T)from 12.0 L to 24.0 L (constant n and T)

D. Volume D. Volume 1) Increases 1) Increases when T changes from 15.0 when T changes from 15.0 °°C to 45.0C to 45.0°°C (constant P and n)C (constant P and n)

18

52

Combined Gas LawCombined Gas Law

PP11VV11 = P= P22VV22

TT11 TT22

OROR

PP11VV11TT22 = P= P22VV22TT11

53

Combined Gas Law ProblemCombined Gas Law Problem

A sample of helium gas has a volume of 0.180 A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 L, a pressure of 0.800 atmatm and a temperature of and a temperature of 2929°°C. What is the new temperature(C. What is the new temperature(°°C) of the C) of the gas at a volume of 90.0 mL and a pressure of gas at a volume of 90.0 mL and a pressure of 3.20 3.20 atmatm??

54

Data TableData Table

Set up Data TableSet up Data Table

PP1 1 = 0.800 = 0.800 atmatm VV11 = 0.180 L= 0.180 L TT11 = 302 K= 302 K

PP22 = 3.20 = 3.20 atmatm VV22= 90.0 mL T= 90.0 mL T2 2 = ??= ????

19

55

CalculationCalculation

Solve for TSolve for T22

TT22 = 302 K x = 302 K x 3.20 3.20 atmatm x x 90.0 mL 90.0 mL = 604 K= 604 K

0.800 0.800 atmatm 180.0 mL180.0 mL

TT22 = 604 K = 604 K -- 273 = 331 273 = 331 °°CC

56

Learning Check Learning Check

True (1) or False(2)True (1) or False(2)

1.___The P exerted by a gas at constant V is not 1.___The P exerted by a gas at constant V is not affected by the T of the gas.affected by the T of the gas.

2.___ At constant P, the V of a gas is directly 2.___ At constant P, the V of a gas is directly proportional to the absolute Tproportional to the absolute T

3.___ At constant T, doubling the P will cause the V 3.___ At constant T, doubling the P will cause the V

of the gas sample to decrease to oneof the gas sample to decrease to one--half its half its

original V.original V.

57

Solution Solution

True (1) or False(2)True (1) or False(2)

1. 1. (2)(2)The P exerted by a gas at constant V is not The P exerted by a gas at constant V is not affected by the T of the gas.affected by the T of the gas.

2. 2. (1)(1) At constant P, the V of a gas is directly At constant P, the V of a gas is directly proportional to the absolute Tproportional to the absolute T

3. 3. (1)(1) At constant T, doubling the P will cause the V At constant T, doubling the P will cause the V

of the gas sample to decrease to oneof the gas sample to decrease to one--half its half its

original V.original V.

20

58

STPSTP

The volumes of gases can be compared when The volumes of gases can be compared when they have the same temperature and pressure they have the same temperature and pressure (STP).(STP).

Standard temperature 0Standard temperature 0°°C or 273 KC or 273 K

Standard pressureStandard pressure 1 1 atmatm (760 mm Hg)(760 mm Hg)