Chapter 13:Chapter 13:GasesGases

What Are Gases?What Are Gases? Gases have Gases have

massmass Much less Much less

compared to compared to liquids and liquids and solids solids

Properties of Properties of GasesGases

Gases are easy Gases are easy to compressto compress

Liquids and Liquids and solids are solids are difficult to difficult to compresscompress

What Are Gases?What Are Gases? Gases fill their Gases fill their

containers containers completelycompletely

Liquids and Liquids and solids have solids have fixed volumesfixed volumes

What Are Gases?What Are Gases? Gases move very quicklyGases move very quickly Movement of gases is called Movement of gases is called

diffusiondiffusion

What Are Gases?What Are Gases? Gases exert pressureGases exert pressure Pressure due to collisionsPressure due to collisions

Kinetic Molecular TheoryKinetic Molecular Theory The behavior of gas is The behavior of gas is

explained by the Kinetic explained by the Kinetic – Molecular theory of – Molecular theory of mattermatter

1. Gases consist of 1. Gases consist of particles that have massparticles that have mass Gases are either Gases are either

monoatomic, diatomic, monoatomic, diatomic, or polyatomic.or polyatomic.

Kinetic Molecular TheoryKinetic Molecular Theory2. There are large distances 2. There are large distances

between gas particlesbetween gas particles– Volume of particles is assumed Volume of particles is assumed

to be zero compared to the to be zero compared to the total volumetotal volume

3. Gas particles are in constant 3. Gas particles are in constant random motionrandom motion

Kinetic Molecular TheoryKinetic Molecular Theory

4. Collisions of gas particles with 4. Collisions of gas particles with other particles or with the walls other particles or with the walls of the container are completely of the container are completely elastic.elastic.

Elastic collision

Kinetic Molecular TheoryKinetic Molecular Theory

5. Kinetic energy of gas depends 5. Kinetic energy of gas depends upon temperatureupon temperature– High temperature, high KEHigh temperature, high KE– Low temperature, low KELow temperature, low KE

6. Gas particles exert no attractive 6. Gas particles exert no attractive forces between one anotherforces between one another

www.falstad.com/gas/www.falstad.com/gas/

Describing Behavior of Describing Behavior of GasesGases

Depends upon 4 variablesDepends upon 4 variables1.1. Amount of Gas (n) – Measured in Amount of Gas (n) – Measured in

Moles (mol)Moles (mol)2.2. Volume (V) – Measure in Liters (L)Volume (V) – Measure in Liters (L)3.3. Temperature (T) – Measured in Temperature (T) – Measured in

Kelvin (K)Kelvin (K)4.4. Pressure (P) – Measured in Pressure (P) – Measured in

Pascals (Pa)Pascals (Pa)

PressurePressure

Pressure is the amount of force Pressure is the amount of force per given area per given area

P = F/AP = F/A One newton of force per square One newton of force per square

meter is the Pascal meter is the Pascal Often measure in kPaOften measure in kPa

Atmospheric PressureAtmospheric Pressure

Pressure exerted by Pressure exerted by the atmospherethe atmosphere

Atmospheric PressureAtmospheric Pressure Air Pressure measured by a Air Pressure measured by a

barometerbarometer Measured in mmHgMeasured in mmHg

Atmospheric PressureAtmospheric Pressure

Air pressure changes with altitudeAir pressure changes with altitude

Atmospheric PressureAtmospheric Pressure Air pressure changes due to the Air pressure changes due to the

heating by the sunheating by the sun

ManometerManometer Enclosed gases may be measured Enclosed gases may be measured

by a manometerby a manometer Pressure of gas = height + air Pressure of gas = height + air

pressurepressure

Units of PressureUnits of Pressure1013.25 millibars (mb) = 1013.25 millibars (mb) =

101.325 kPa = 1 atmosphere 101.325 kPa = 1 atmosphere (atm) = 14.7 pounds per in(atm) = 14.7 pounds per in22 (psi) = 760 mm of Hg (torr)(psi) = 760 mm of Hg (torr)

PracticePracticeHigh Pressure 1085 mb in High Pressure 1085 mb in

Mongolia (2001) Convert to kPaMongolia (2001) Convert to kPaLow Pressure 870 mb in a Pacific Low Pressure 870 mb in a Pacific

Typhoon (1979) Convert to AtmTyphoon (1979) Convert to Atm

Boyle’s LawBoyle’s Law The pressure and volume of a The pressure and volume of a

sample of gas are inversely sample of gas are inversely proportional at constant proportional at constant temperaturetemperature

““spring of air”spring of air” PP11VV11=P=P22VV22

PracticePractice A weather balloon contains 150. L A weather balloon contains 150. L

of gas, internal gas pressure is 1.0 of gas, internal gas pressure is 1.0 atm. Atmospheric pressure at 41 atm. Atmospheric pressure at 41 km is 0.4 atm. Calculate the new km is 0.4 atm. Calculate the new volume of the balloon.volume of the balloon.

2.00 L of a gas is at 740.0 mmHg 2.00 L of a gas is at 740.0 mmHg pressure. What is its volume at pressure. What is its volume at standard pressure? standard pressure?

Charles’s LawCharles’s Law At constant pressure, the volume At constant pressure, the volume

of a fixed amount of gas is directly of a fixed amount of gas is directly proportional to its temperature.proportional to its temperature.

Helped determine absolute zeroHelped determine absolute zero VV11/T/T11=V=V22/T/T22

All temperatures must be All temperatures must be converted to Kelvinconverted to Kelvin

PracticePractice What will be the volume of a gas What will be the volume of a gas

sample at 355 K if its volume at sample at 355 K if its volume at 273 K is 8.57 Liters?273 K is 8.57 Liters?

At constant pressure a gas can be At constant pressure a gas can be used as a thermometer. A sample used as a thermometer. A sample of gas has a volume of 1 L at -18 of gas has a volume of 1 L at -18 00C. What is the temperature if the C. What is the temperature if the volume of the same gas is volume of the same gas is changed to 0.45 Liters?changed to 0.45 Liters?

Avogadro's LawAvogadro's Law Avogadro’s LawAvogadro’s Law states equal states equal

volumes of gases at the same volumes of gases at the same temperature and pressure temperature and pressure contain an equal number of contain an equal number of particles.particles.

Molar volume 22.4 L at STP.Molar volume 22.4 L at STP.

Dalton’s LawDalton’s Law Dalton’s Law of Partial Dalton’s Law of Partial

Pressure Pressure states that the sum of states that the sum of the partial pressures of all of the the partial pressures of all of the components in a gas mixture is components in a gas mixture is equal to the total pressure of the equal to the total pressure of the gas mixture.gas mixture.

PPTT = P = Paa + P + Pbb + P + Pcc …. ….

PracticePractice What is atmospheric pressure if the What is atmospheric pressure if the

partial pressures of Npartial pressures of N22, O, O22, and Ar are , and Ar are 604.5 mm Hg, 162.8 mm Hg, and 0.5 604.5 mm Hg, 162.8 mm Hg, and 0.5 mm Hg respectively?mm Hg respectively?

The gases of carbon dioxide, oxygen, The gases of carbon dioxide, oxygen, nitrogen, neon, and krypton are nitrogen, neon, and krypton are mixed in a container. All gases have mixed in a container. All gases have the same partial pressure and the the same partial pressure and the total pressure is 33,500 Pa. What is total pressure is 33,500 Pa. What is the partial pressure of nitrogen?the partial pressure of nitrogen?

Ideal Gas vs. Real Ideal Gas vs. Real GasGas

An An Ideal GasIdeal Gas represents a gas as represents a gas as described by the kinetic-molecular described by the kinetic-molecular theory.theory.

Assumes no interaction between Assumes no interaction between gas moleculesgas molecules

All gases are All gases are Real GasReal Gas An ideal gas behaves >95% like a An ideal gas behaves >95% like a

real gas.real gas. Real Gases deviate from ideal Real Gases deviate from ideal

gases at low temperatures and gases at low temperatures and high pressures.high pressures.

Ideal Gas LawIdeal Gas Law The ideal gas law combines all The ideal gas law combines all

variables involved in a gas.variables involved in a gas.

PV = nRTPV = nRT R is a constantR is a constant R = 0.0821 atm-L/mol-KR = 0.0821 atm-L/mol-K Temp must be in KTemp must be in K Pressure must be in AtmPressure must be in Atm Volume must be in LitersVolume must be in Liters

PracticePractice How many moles of a gas at 100 How many moles of a gas at 100

ooC does it take to fill a 1.00 Liter C does it take to fill a 1.00 Liter flask to a pressure of 1.50 atm?flask to a pressure of 1.50 atm?

What is the volume occupied by What is the volume occupied by 9.45 g of C9.45 g of C22HH22 at STP? at STP?

How many kilograms of oxygen How many kilograms of oxygen gas are contained in a sample that gas are contained in a sample that occupies 505 L at 675 kPa and -15 occupies 505 L at 675 kPa and -15 ooC?C?