IT’S A GAS… Gases have some interesting characteristics that have fascinated scientists for 300...

IT’S A GAS…IT’S A GAS…

Gases have some interesting Gases have some interesting characteristics that have fascinated characteristics that have fascinated scientists for 300 years.scientists for 300 years.

The first gas to be studied was The first gas to be studied was air air & it & it was a long time before it was discovered was a long time before it was discovered that air was actually a mixture of that air was actually a mixture of particles rather than a particles rather than a single gas.single gas.• But this realization did not make the But this realization did not make the

study of gas behavior more difficult.study of gas behavior more difficult.• Although air is a mixture of several Although air is a mixture of several

different gases, it behaves much the different gases, it behaves much the same as any single gas.same as any single gas.

Gases have some interesting Gases have some interesting characteristics that have fascinated characteristics that have fascinated scientists for 300 years.scientists for 300 years.

The first gas to be studied was The first gas to be studied was air air & it & it was a long time before it was discovered was a long time before it was discovered that air was actually a mixture of that air was actually a mixture of particles rather than a particles rather than a single gas.single gas.• But this realization did not make the But this realization did not make the

study of gas behavior more difficult.study of gas behavior more difficult.• Although air is a mixture of several Although air is a mixture of several

different gases, it behaves much the different gases, it behaves much the same as any single gas.same as any single gas.

The Nature of GasesThe Nature of Gases

Regardless of their chemical Regardless of their chemical identity, gases tend to exhibit identity, gases tend to exhibit similar similar physical behaviorsphysical behaviors

Gas particles can be monatomic Gas particles can be monatomic (Ne), diatomic (N(Ne), diatomic (N22), or polyatomic ), or polyatomic (CH(CH44) – but they all have some ) – but they all have some common characteristics:common characteristics:

The Nature of GasesThe Nature of Gases

1.1. Gases have Gases have massmass..2.2. Gases are compressible.Gases are compressible.3.3. Gases Gases fillfill their containers. their containers.4.4. Gases diffuse.Gases diffuse.5.5. Gases Gases exert pressureexert pressure..6.6. Pressure is related to Pressure is related to

TemperatureTemperature

Kinetic Molecular TheoryKinetic Molecular Theory There is a theory that modern day There is a theory that modern day

chemist’s use to explain the chemist’s use to explain the behaviors and characteristics of behaviors and characteristics of ideal gases - the Kinetic Molecular ideal gases - the Kinetic Molecular Theory of Matter.Theory of Matter.

• The theory states that the tiny The theory states that the tiny particles in all forms of matter particles in all forms of matter are in continuous motion.are in continuous motion.

There are There are 33 basic assumptions of basic assumptions of the KMT as it applies to ideal the KMT as it applies to ideal gases.gases.

• Ideal gases are “perfect” gases Ideal gases are “perfect” gases that are used as a model to that are used as a model to describe characteristics of real describe characteristics of real gases.gases.

KMT Assumption #1KMT Assumption #1 A gas is composed ofA gas is composed of small hardsmall hard

particlesparticles.. The particles have an insignificant The particles have an insignificant

volume and are relatively far volume and are relatively far apart from one apart from one another.another.

There isThere is empty spaceempty space between particles.between particles.

No attractive or repulsive No attractive or repulsive forces between particles. forces between particles.

The particles in a gas move inThe particles in a gas move in constant random motionconstant random motion..

Particles move in straight paths Particles move in straight paths and are completely independent and are completely independent of each of otherof each of other

Particles path is only Particles path is only changed by changed by colliding colliding with with another particle another particle or the sides or the sides of its container.of its container.

KMT Assumption #2KMT Assumption #2

Molecular motionMolecular motion

All collisions a gas particle All collisions a gas particle undergoes areundergoes are perfectlyperfectly elastic.elastic.

They exert a pressure but don’t They exert a pressure but don’t lose any energy during the lose any energy during the collisions.collisions.

KMT Assumption #3KMT Assumption #3

The Kinetic Molecular Theory

The Kinetic Molecular Theory

Gases seem weightless, but Gases seem weightless, but they are classified as they are classified as mattermatter, , therefore, they must have therefore, they must have mass.mass.

The The densitydensity of a gas is much of a gas is much less than the density of a less than the density of a liquid or solid.liquid or solid.• It’s this very low density that It’s this very low density that

allows us to be able to walk allows us to be able to walk through the room without through the room without concerning ourselves with air concerning ourselves with air resistance.resistance.

The mass is really only The mass is really only noticeable if we have a noticeable if we have a collectioncollection of gas in a of gas in a container.container.

Gases have mass.Gases have mass.

Gas particles have a high velocity, Gas particles have a high velocity, relative to their low masses. relative to their low masses.•Which means they have a great Which means they have a great

deal of kinetic energydeal of kinetic energy•This high velocity and low mass This high velocity and low mass

means the particles are spread means the particles are spread far apart, with empty far apart, with empty space in between particles.space in between particles.

Therefore, if you Therefore, if you squeezesqueeze on a on a gas, its volume can be gas, its volume can be reduced considerablyreduced considerably

Gases “R” squeezableGases “R” squeezable

Gases “R” squeezableGases “R” squeezable The gas particles empty space The gas particles empty space

can be compressed by added can be compressed by added pressure giving the gas pressure giving the gas particles less room to bounce particles less room to bounce around thus around thus decreasingdecreasing the the overall volume.overall volume.•Compression allows us to Compression allows us to

package a lot of gas in a package a lot of gas in a relatively small volume.relatively small volume.

•And compression generates And compression generates a spring like character a spring like character to to develop to the gas develop to the gas collection collection

Gases “R” squeezableGases “R” squeezable There are a huge number of There are a huge number of

applicationsapplications• Storm door closersStorm door closers• Pneumatic tube delivery devicesPneumatic tube delivery devices• TiresTires• Air tanksAir tanks• Etc…Etc…

Gases fill their containersGases fill their containers Gases Gases expandexpand until they take up until they take up

as much room as they possibly as much room as they possibly can.can.

Gases spread out to fill containers Gases spread out to fill containers until until the concentration the concentration of gases is of gases is uniform uniform throughout the throughout the entire entire space.space.

This is why that This is why that nowhere around you nowhere around you is there an is there an absence absence of air. of air.

Gases fill their containersGases fill their containers Since the particles are in constant Since the particles are in constant

random motion,random motion, according to the according to the KMT, then the gases move in a KMT, then the gases move in a straight line until they collide straight line until they collide with other particles or the sides with other particles or the sides of the container, which causes of the container, which causes them to change directions until them to change directions until they collide with something else.they collide with something else.

This random bouncing motion, This random bouncing motion, allows for the mixing up allows for the mixing up and spreading of the and spreading of the particles until they are particles until they are uniformuniform throughout throughout the entire container. the entire container.

Gases diffuseGases diffuse Gases can move through each Gases can move through each

other rapidly.other rapidly.• The movement of one substance The movement of one substance

through another is called through another is called diffusion.diffusion.

Because of all of the empty space Because of all of the empty space between gas molecules, gas between gas molecules, gas molecules can molecules can pass betweenpass between each each other until each gas is mixed other until each gas is mixed evenly throughout the entire evenly throughout the entire container.container.

Since gases are in constant Since gases are in constant random motion, they are moving random motion, they are moving and colliding with everything and colliding with everything around them, and there is so much around them, and there is so much empty space, empty space, the gases mix the gases mix uniformly.uniformly.

Gases diffuseGases diffuse

Gases diffuseGases diffuse This doesn’t happen at the same This doesn’t happen at the same

speedsspeeds for all gases. for all gases.•Some gases diffuse more rapidly Some gases diffuse more rapidly then other gases based on their then other gases based on their size and their energy.size and their energy.

•KE=1/2mvKE=1/2mv22

Diffusion explains why gases are Diffusion explains why gases are able to spread out to fill their able to spread out to fill their containers.containers.

It’s why we can all breath oxygen It’s why we can all breath oxygen anywhere in the room. anywhere in the room.

Gases exert pressureGases exert pressure Gas particles exert Gas particles exert pressurepressure by by

colliding with objects in their path.colliding with objects in their path. The The sumsum of all of the collisions of all of the collisions

makes up the pressure the gas makes up the pressure the gas exerts.exerts.

The KMT says since they are in The KMT says since they are in constant random motion, the constant random motion, the particles will colliding with particles will colliding with anything in their path.anything in their path.

The definition of pressure is The definition of pressure is the the force per unit areaforce per unit area – – so the total of so the total of all of the tiny collisions all of the tiny collisions makes up the pressure exer- makes up the pressure exerted by the gas ted by the gas

Gases exert pressureGases exert pressureIt’s the pressure exerted by the It’s the pressure exerted by the gases that hold the walls of a gases that hold the walls of a container outcontainer outThe pressure of gases is what The pressure of gases is what keeps our tires inflated, makes our keeps our tires inflated, makes our basketballs bounce, makes basketballs bounce, makes hairspray come out of the can, hairspray come out of the can, helps our lungs inflate, allow helps our lungs inflate, allow vacuum cleaners to vacuum cleaners to work, etc.work, etc.

Pressure depends on TempPressure depends on Temp The average kinetic energy of the The average kinetic energy of the

particles that make up an object is particles that make up an object is defined as temperature.defined as temperature.• Therefore, the higher the Therefore, the higher the

temperaturetemperature the more the more energyenergy the gas particle has.the gas particle has.

So the collisions are more often So the collisions are more often and with a higher force.and with a higher force.

And since pressure is a function of And since pressure is a function of force, the pressure increases force, the pressure increases inside the container.inside the container.• Think about the pressure of a set Think about the pressure of a set

of tires on a car.of tires on a car.

Pressure depends on TempPressure depends on Temp

Pressure Gauge

Pressure Gauge

Today’s temp: 35°FToday’s temp: 35°F

Today’s temp: 85°FToday’s temp: 85°F

Pressure depends on TempPressure depends on Temp

Pressure Gauge

Pressure Gauge

Characteristics of GasesCharacteristics of Gases

Measuring GasesMeasuring Gases The conditions under which a gas The conditions under which a gas

is studied is very is studied is very important to its behavior.important to its behavior.

Experimental work in chemistry Experimental work in chemistry requires the measurement of requires the measurement of such quantities as such quantities as volumevolume, , temperaturetemperature, , pressurepressure, , and the and the amount of sampleamount of sample..

These quantities are called These quantities are called variables and if they are not variables and if they are not accounted for then the results of accounted for then the results of the experiment might be the experiment might be jeopardized.jeopardized.

Amount (n)Amount (n) The quantity of gas in a given The quantity of gas in a given

sample is generally given in sample is generally given in terms of terms of moles of gas.moles of gas.• This of course is in terms of This of course is in terms of 6.02 6.02

x 10x 102323 molecules per mole of the molecules per mole of the gas.gas.

Don’t forget to convert mass to Don’t forget to convert mass to moles you just divide by the moles you just divide by the molar massmolar mass of the gas. of the gas.

So amount of So amount of a gas, refers to a gas, refers to how many how many gas gas particles are in particles are in the sample. the sample.

Volume (V)Volume (V) The volume of a gas is simply the The volume of a gas is simply the

volume of the container it is volume of the container it is contained in.contained in.

The metric unit of volume, liter The metric unit of volume, liter (L), is often used.(L), is often used.

There might also be problems There might also be problems that use cubic meters that use cubic meters as the unit for as the unit for volume.volume.•1000 L = 1 m1000 L = 1 m33

Temperature (T)Temperature (T) The temperature of a gas is The temperature of a gas is

generally measured with a generally measured with a thermometer thermometer in Celsius. in Celsius.

All calculations involving gases All calculations involving gases should be made after converting should be made after converting the Celsius to Kelvin the Celsius to Kelvin temperature.temperature.Kelvin = C° +

273Kelvin = C° +

273Celsius = K - 273

Celsius = K - 273

Temperature (T)Temperature (T)

Pressure (Pressure (PP)) The pressure of a gas is the force The pressure of a gas is the force

exerted on the wall of the exerted on the wall of the container, in which a gas is container, in which a gas is trapped.trapped.

There are several units for There are several units for pressure depending on the pressure depending on the instrument used to measure it instrument used to measure it including:including: 1) atmospheres 1) atmospheres

((atmatm)) 2) Millimeters of Mercury 2) Millimeters of Mercury ( (mmHgmmHg))

3) Kilopascal (3) Kilopascal (kPakPa))

S T PS T PS T PS T P The behavior of a gas depends The behavior of a gas depends

very strongly on the very strongly on the temperature and the pressure temperature and the pressure at which the gas is held.at which the gas is held.

To make it easier to discuss the To make it easier to discuss the behavior of a gas, it is behavior of a gas, it is convenient to designate a set of convenient to designate a set of standard conditionsstandard conditions, called STP. , called STP. •Standard Temp and Standard Standard Temp and Standard

PressurePressure•Standard Temperature = Standard Temperature = 0°C or 0°C or

273K273K•Standard Pressure = Standard Pressure = 1atm or 1atm or

760mmHg or 101.3kPa760mmHg or 101.3kPa (depending on the method of (depending on the method of measure)measure)

Atmospheric PressureAtmospheric PressureAtmospheric PressureAtmospheric Pressure The gases in the air are exerting The gases in the air are exerting

a pressure called atmospheric a pressure called atmospheric pressurepressure

Atmospheric pressure is a Atmospheric pressure is a result of the fact that result of the fact that air has air has massmass is is and is colliding with and is colliding with everything under the sun everything under the sun with a force with a force..

Atmospheric pressure is Atmospheric pressure is measured with a measured with a barometer.barometer.

Atmospheric PressureAtmospheric PressureAtmospheric PressureAtmospheric Pressure

Atmospheric pressure varies with altitude

•The lower the altitude, the longer and heavier is the column of air above an area of the earth.

Look on the back of a box of cake mix for the difference in baking times based on the atmospheric pressure in your region.


Knowing this atmosphericatmospheric pressure and predicting changes in the atmospheric pressure is how forecasters predict the weather.

Low pressure or dropping pressure indicates a change of weather from fair to rain.

High pressure is an ind- ication of clear skies & sun.


Measuring GasesMeasuring GasesMeasuring GasesMeasuring Gases

Gas LawsGas Laws Studies of the behavior of gases Studies of the behavior of gases

played a major role in the played a major role in the development of physical sciences development of physical sciences in the 7in the 7thth and 8 and 8thth centuries. centuries.

The The Kinetic MolecularKinetic Molecular theory theory marked a significant achievement marked a significant achievement in understanding the behavior of in understanding the behavior of gases.gases.

Observations have become Observations have become mathematical laws which we can mathematical laws which we can use to use to predict predict quantitative quantitative outcomes.outcomes.

Boyle’s LawBoyle’s Law Robert Boyle was among the first Robert Boyle was among the first

to note the inverse relationship to note the inverse relationship between between pressurepressure and and volumevolume of of a gas.a gas.•As the pressure on a gas As the pressure on a gas increased the volume of the gas increased the volume of the gas will decrease.will decrease.

He measured the volume He measured the volume of air at different of air at different pressures, pressures, and observed a pattern of and observed a pattern of behavior. behavior.•During his experimentsDuring his experiments TemperatureTemperature andand amount amount of gas of gas weren’t allowed to weren’t allowed to changechange

1621-16911621-1691

Boyle’s LawBoyle’s Law

How does Pressure and Volume of gases relate

graphically?

How does Pressure and Volume of gases relate

graphically?

Volu

me

Volu

me

PressurePressure

PV = kPV = k

Temperature, # of particlesremain constant

Temperature, # of particlesremain constant

Boyle’s Mathematical Law:Boyle’s Mathematical Law:

since PV equals a constantsince PV equals a constant

PP11VV11 = = PP22VV22

PP11VV11 = = PP22VV22

Ex: A gas has a volume of 3.0 L Ex: A gas has a volume of 3.0 L at 2 atm. What will its volume at 2 atm. What will its volume

be at 4 atm?be at 4 atm?

If we have a given amount of a gas at If we have a given amount of a gas at a starting pressure and volume, what a starting pressure and volume, what would happen to the pressure if we would happen to the pressure if we

changed the volume? changed the volume? Or to the volume if we changed the Or to the volume if we changed the

pressure? pressure?

Boyle’s Mathematical Law:Boyle’s Mathematical Law:

1)1)List the variables or clues given:List the variables or clues given:

2)2)determine which law is being determine which law is being represented:represented:

PP11 = 2 atm = 2 atm VV11 = 3.0 L = 3.0 L

PP22 = 4 atm = 4 atm VV22 = ? = ?

P1V1 = V2 P2

3) Plug in the variables & calculate:3) Plug in the variables & calculate:

(2 atm)(2 atm)(3.0 L) =(3.0 L) =(4 atm)(4 atm)(V(V22))

Charles’s LawCharles’s Law Jacques Charles studied the Jacques Charles studied the

direct mathematical relationship direct mathematical relationship between between temp-eraturetemp-erature and and volumevolume of a gas. of a gas.•As temperature increases the As temperature increases the volume of the gas increasesvolume of the gas increases

Charles measured the volume of Charles measured the volume of air at different temperatures, air at different temperatures, and recorded the and recorded the results.results.•During his experimentsDuring his experiments pressurepressure of the system of the system andand amount of gasamount of gas were held were held constant.constant.

1746-18231746-1823

Charles’ LawCharles’ Law

Temp

How does Temperature and Volume of gases relate

graphically?

How does Temperature and Volume of gases relate

graphically?V

olu

me V/T = k

Pressure, # of particlesremain constant

Pressure, # of particlesremain constant

Charles’ LawCharles’ Law

Charles’s Mathematical Law:Charles’s Mathematical Law:

since V/T = ksince V/T = k

Ex: A gas has a volume of 3.0 L Ex: A gas has a volume of 3.0 L at 400K. What is its volume at at 400K. What is its volume at

500K?500K?

==VV11 V V22

TT11 T T22

If we have a given amount of a gas at If we have a given amount of a gas at a starting volume and temperature, a starting volume and temperature, what would happen to the volume if what would happen to the volume if

we changed the temperature? we changed the temperature? Or to the temperature if we changed Or to the temperature if we changed

the volume? the volume?

Charles’s Mathematical Law:Charles’s Mathematical Law:

2)2)determine which determine which law is being law is being represented:represented:

TT11 = 400K = 400K VV11 = 3.0 L = 3.0 L

TT22 = 500K = 500K VV22 = ? = ?


VV11VV11

TT11TT11

VV22VV22

TT22TT22

====

3) Plug in the 3) Plug in the variables & variables & calculate:calculate:

3.0L3.0L

400K400K 500K500K

X LX L==

Gay-Lussac’s LawGay-Lussac’s Law Old man Lussac studied the Old man Lussac studied the

direct relationship between direct relationship between temperaturetemperature and and pressurepressure of a of a gas.gas.• As the temperature increases the As the temperature increases the

press-ure a gas exerts on its press-ure a gas exerts on its container increases.container increases.

During his experiments During his experiments volume of the volume of the system and system and amount of gas were held amount of gas were held constant. constant.

1778-18501778-1850

Gay-Lussac’s LawGay-Lussac’s Law

Temp

Pre

ssu

re

How does Pressure and Temperature of gases relate

graphically?

How does Pressure and Temperature of gases relate

graphically?

P/T = k

Volume, # of particlesremain constant

Volume, # of particlesremain constant

since P/T = ksince P/T = k

PP11 PP22TT11 T T22

==

Ex: A gas has a pressure of Ex: A gas has a pressure of 3.0atm at 400K. What is 3.0atm at 400K. What is

its pressure at 500K?its pressure at 500K?

If we have a given amount of a gas at If we have a given amount of a gas at a starting temperature and pressure, a starting temperature and pressure, what would happen to the pressure if what would happen to the pressure if

we changed the temperature? we changed the temperature? Or to the temp. if we changed the Or to the temp. if we changed the

pressure? pressure?

Gay-Lussac’s Mathematical Law:Gay-Lussac’s Mathematical Law:

Gay-Lussac’s Mathematical Law:Gay-Lussac’s Mathematical Law:

2)2)determine which determine which law is being law is being represented:represented:

TT11 = 400K = 400K PP11 = 3.0 atm = 3.0 atm

TT22 = 500K = 500K PP22 = ? = ?


P1P1

TT11

PP22

TT22

==

3) Plug in the 3) Plug in the variables & variables & calculate:calculate:

3.0atm

400K400K 500K500K

X LX L==

LAWLAW RELAT-RELAT-IONSHIPIONSHIP LAWLAW CON-CON-

STANTSSTANTS

Boyle’sBoyle’s PP V V PP11VV1 1 = P= P22VV22 T, nT, n

CharlesCharles’’

VV T T VV11/T/T11 = V = V22/T/T22 P, nP, n

Gay-Gay-Lussac’Lussac’

ssPP T T PP11/T/T11 = P = P22/T/T22 V, nV, n

Summary of the Named Gas-Laws:Summary of the Named Gas-Laws:

Combined Gas LawCombined Gas Law

Class WorkClass Work

1)1) A balloon contains 30.0 L of He gas at 103kPa. A balloon contains 30.0 L of He gas at 103kPa. What is the volume of He when the balloon rises What is the volume of He when the balloon rises to an altitude where the pressure is only 25.0kPa?to an altitude where the pressure is only 25.0kPa?

2)2) A balloon inflated in a room at 24.0˚C has a volume A balloon inflated in a room at 24.0˚C has a volume of 4.00 L. The balloon is heated to a temperature of 4.00 L. The balloon is heated to a temperature of 58.0˚C. What is the new volume?of 58.0˚C. What is the new volume?

3)3) A sample of NA sample of N22(g) is at STP. What will the pressure (g) is at STP. What will the pressure (in atm) be if the temp is increased to 373K?(in atm) be if the temp is increased to 373K?

4)4) The volume of a gas-filled balloon is 30.0L at The volume of a gas-filled balloon is 30.0L at 98.0˚C and 1147 mmHg. What would the volume 98.0˚C and 1147 mmHg. What would the volume be at STP?be at STP? 1) 156 L 2) 4.46 L 3) 1.37 atm 4) 33.3 L 1) 156 L 2) 4.46 L 3) 1.37 atm 4) 33.3 L

IT’S A GAS… Gases have some interesting characteristics that have fascinated scientists for 300...

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