Chapter 13:Chapter 13:GasesGases

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

massmass

Properties of Properties of GasesGases

Easy to Easy to compresscompress

What Are Gases?What Are Gases? Fill their Fill their

containers containers completelycompletely

What Are Gases?What Are Gases? Move very quicklyMove 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 is due to collisionsPressure is due to collisions

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 per given Pressure is the amount of force per given areaarea

One newton of force per square meter is One newton of force per square meter is the Pascal the Pascal

Often measure in kPaOften measure in kPa 1013.25 millibars (mb) = 101.325 1013.25 millibars (mb) = 101.325

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

Atmospheric PressureAtmospheric Pressure

Pressure exerted by Pressure exerted by the atmospherethe atmosphere

Atmospheric PressureAtmospheric Pressure

Air Air Pressure Pressure measured measured by a by a barometerbarometer

Measured Measured in mmHgin mmHg

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

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

by the K–M theory of matterby the K–M theory of matter1.1. Gases consist of particles that Gases consist of particles that

have masshave mass2. There are large distances 2. There are large distances

between gas particlesbetween gas particles3. 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

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/

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

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 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.

A sample of gas has a volume of 1 A sample of gas has a volume of 1 L at -18 L at -18 00C. What is the C. What is the temperature if the volume of the temperature if the volume of the same gas is changed to 0.45 Liters?same gas is changed to 0.45 Liters?

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?

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?

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 …. ….

Combined Gas LawCombined Gas LawWe can take all of the pressure-

volume-temperature relationships we’ve just talked about and combine them into one gas law:(P1V1)/T1 = (P2V2)/T2

If you remember this gas law, you can figure out the others.

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?

If I have 21 liters of gas held at a pressure of 78 atm and a temperature of 900. K, what will be the volume of the gas if I decrease the pressure to 45 atm and decrease the temperature to 750 K?

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

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.

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?

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

Guy Lussac’s LawGuy Lussac’s Law At constant volume, the pressure At constant volume, the pressure

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

PP11/T/T11=P=P22/T/T22

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

AutoclavesAutoclaves

PracticePracticeYou fill your car tires to 35 psi in

the summer when it’s 31 °C. At Thanksgiving, when it’s -7 °C, you notice that your tire is low. What is the pressure inside your tires?

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 contain temperature and pressure contain an equal number of particles.an equal number of particles.

Volume and amount are directly Volume and amount are directly proportional.proportional.

VV11//nn11 = V = V22//nn22

PracticePractice The gases of carbon dioxide, The gases of carbon dioxide,

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

PracticePractice I have an unknown volume of gas at a

pressure of 0.5 atm and a temperature of 325 K. If I raise the pressure to 1.2 atm, decrease the temperature to 320 K, and measure the final volume to be 48 liters, what was the initial volume of the gas?

If I have 21 liters of gas held at a pressure of 78 atm and a temperature of 900 K, what will be the volume of the gas if I decrease the pressure to 45 atm and decrease the temperature to 750 K?