General Properties of GasesGeneral Properties of Gases

There is a lot of “free” space There is a lot of “free” space in a gas.in a gas.

Gases can be expanded Gases can be expanded infinitely.infinitely.

Gases fill containers uniformly Gases fill containers uniformly and completely.and completely.

Gases diffuse and mix rapidly.Gases diffuse and mix rapidly.

PressurePressureThe result of a force distributed over an area.The result of a force distributed over an area.

SI unit for pressure = pascal (Pa) = N/mSI unit for pressure = pascal (Pa) = N/m22

(one kilopascal = kPa= 1000 Pa)(one kilopascal = kPa= 1000 Pa)

Atmospheric PressureAtmospheric PressureThe pressure the earth’s atmosphere exerts The pressure the earth’s atmosphere exerts due to its weight. due to its weight.

PressurePressure

Pressure of air is measured Pressure of air is measured with a with a BAROMETERBAROMETER

Column height measures Column height measures Pressure of atmospherePressure of atmosphere

1 standard atmosphere (atm) 1 standard atmosphere (atm)

= 760 mm Hg = 101.3 kPa (SI = 760 mm Hg = 101.3 kPa (SI unit is PASCAL) unit is PASCAL)

Measuring Pressure of Measuring Pressure of confined gasconfined gas

Manometer- Instrument used Manometer- Instrument used to measure gas pressureto measure gas pressure

Filled with MercuryFilled with Mercury

Variables that Affect the Properties Variables that Affect the Properties of Gases CHEMSAVER P. 31of Gases CHEMSAVER P. 31

P = pressure (atm, mmHg, kPa)P = pressure (atm, mmHg, kPa)

V = volume (ml, L, cmV = volume (ml, L, cm33, etc), etc)

T = temperature (K) T = temperature (K) K = K = 00C + 273C + 273

–ALL temperatures MUST be ALL temperatures MUST be in Kelvin to calculate other in Kelvin to calculate other variables!!! No Exceptions!variables!!! No Exceptions!

n = amount (moles)n = amount (moles)

Standard ConditionsStandard ConditionsSTP- STP- SStandard tandard TTemperature and emperature and PPressureressure

Standard Temperature: Standard Temperature: 273 K273 K

Standard Pressure: Standard Pressure: 1.00 atm 1.00 atm (atmosphere)(atmosphere)

Pressure ConversionsPressure Conversions

1.00 atm = 101.3 kPa1.00 atm = 101.3 kPa

1.00 atm = 760. mmHg1.00 atm = 760. mmHg

101.3kPa = 760. mmHg101.3kPa = 760. mmHg

Pressure ConversionsPressure Conversions

A. What is 475 mm Hg expressed in atm?A. What is 475 mm Hg expressed in atm?

1.00 atm1.00 atm

760 mm Hg760 mm Hg

B. The pressure of a tire is measured as 29.4 kPa.B. The pressure of a tire is measured as 29.4 kPa.

What is this pressure in mm Hg?What is this pressure in mm Hg?

760 mm Hg 760 mm Hg

101.3kPa101.3kPa = 221 mm Hg

= 0.625 atm475 mm Hg x

29.4 kPa x

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Pressure and Volume

Pressure and VolumePressure and Volume

When temperature and the # of particles are When temperature and the # of particles are kept constant in a closed container:kept constant in a closed container:

As Volume decreases, PressureAs Volume decreases, Pressure

oror

As Volume increases, Pressure As Volume increases, Pressure

This is an relationshipThis is an relationship

increases

inverse

decrease

A Graph of Boyle’s LawA Graph of Boyle’s Law

Boyle’s LawBoyle’s LawP P αα 1/V 1/V

This means Pressure and This means Pressure and

Volume are INVERSELY Volume are INVERSELY PROPORTIONAL if moles PROPORTIONAL if moles

and temperature are constant and temperature are constant

(do not change). For example, (do not change). For example,

P goes up as V goes down.P goes up as V goes down.

PP1 1 • V• V11 = = PP2 2 • V• V22

Robert Boyle Robert Boyle (1627-1691)(1627-1691)

Boyle’s LawBoyle’s LawIf the gas is compressed to half the volume it If the gas is compressed to half the volume it had, twice as many molecules are present in had, twice as many molecules are present in any given volume.any given volume.

Twice as many impacts per second on the walls Twice as many impacts per second on the walls of the container results in doubling the of the container results in doubling the pressure.pressure.

Boyle’s Law ExampleBoyle’s Law ExampleA balloon filled with Helium has a volume of A balloon filled with Helium has a volume of 457ml at standard atmospheric pressure. After 457ml at standard atmospheric pressure. After the balloon is released, it reaches an altitude of the balloon is released, it reaches an altitude of 6.3km where the pressure is only 65.5kPa. 6.3km where the pressure is only 65.5kPa. What is the volume of the balloon at this What is the volume of the balloon at this altitude?altitude?

PP11 • V • V11 = P = P22 • V • V22

Temperature and Volume

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Volume and TemperatureVolume and Temperature

Pressure and the # of particles are constant thenPressure and the # of particles are constant then

As Temperature As Temperature decreasesdecreases, Volume _________ , Volume _________

ororAs Temperature As Temperature increasesincreases, Volume __________, Volume __________

This is a relationshipThis is a relationshipdirect

decreases

increases

A Graph of Charles’s LawA Graph of Charles’s Law

Charles LawCharles LawIf n (moles) and P are constant, If n (moles) and P are constant,

then V then V αα T T

V and T are directly proportional.V and T are directly proportional.

If one temperature goes up, the volume If one temperature goes up, the volume goes up!goes up!

VV11 VV22

TT11 T T22

=

Jacques Charles Jacques Charles (1746-1823)(1746-1823)

VV11TT22 V V22TT11=

Charles’ Law Example Charles’ Law Example A quantity of gas occupies a volume of 506 cmA quantity of gas occupies a volume of 506 cm33 at a temperature of 147at a temperature of 147ooC. Assuming that the C. Assuming that the pressure remains constant, at what pressure remains constant, at what temperature will the volume of the gas be 604 temperature will the volume of the gas be 604 cmcm33??

VV11 = 506cm = 506cm33 VV22= 604cm= 604cm33

TT11 = 147 = 147ooC + 273 =C + 273 = 420K420K TT22= ??= ??

Charles’ LawCharles’ LawDoubling the Kelvin temperature of a gas Doubling the Kelvin temperature of a gas makes the gas expand resulting in makes the gas expand resulting in doubling the volume of the gasdoubling the volume of the gas

Pressure and TemperaturePressure and Temperature

Volume and the # of particles are constant then:Volume and the # of particles are constant then:

As Temperature As Temperature decreasesdecreases, pressure _______ , pressure _______

oror

As Temperature As Temperature increasesincreases, pressure ________, pressure ________

This is a relationshipThis is a relationship

increase

decrease

direct

Gay-Lussac’s LawGay-Lussac’s Law

If n and V are constant, If n and V are constant, then P then P αα T T

P and T are directly proportional.P and T are directly proportional.

If one temperature goes up, the pressure goes If one temperature goes up, the pressure goes up!up!

=PP11TT22 P P22TT11PP11 PP22

TT11 T T22

=

Guy Lussac’s LawGuy Lussac’s Law

Doubling the Kelvin temperature of a gas Doubling the Kelvin temperature of a gas doubles the average kinetic energy of its doubles the average kinetic energy of its molecules.molecules.

Faster moving molecules strike the wall of Faster moving molecules strike the wall of the container more often and with more the container more often and with more force doubling the Pressure.force doubling the Pressure.

Gas Pressure Temperature Volume

Law (P) (T) (V)

Boyles constant

Charles constant

Gay-

Lussac constant

CHEMSAVER P 31