GasesGases

Ch.10 and 11Ch.10 and 11

Kinetic-Molecular TheoryKinetic-Molecular Theory

1.1. Gases consist of very small particles Gases consist of very small particles that are far apartthat are far apart

Most particles are moleculesMost particles are molecules

Volume of particles = 0 because total Volume of particles = 0 because total volume of gas is very largevolume of gas is very large

Kinetic-Molecular TheoryKinetic-Molecular Theory

2.2. Collisions are “elastic” – no net loss Collisions are “elastic” – no net loss of total energyof total energy

3.3. Particles in constant, rapid, random Particles in constant, rapid, random motionmotion

Fill containers easily, overcome attractive Fill containers easily, overcome attractive forces between themforces between them

Kinetic-Molecular TheoryKinetic-Molecular Theory4.4. Particles have no attraction or Particles have no attraction or

repulsion to each other repulsion to each other

5.5. Temperature of gas depends on Temperature of gas depends on average kinetic energy of particlesaverage kinetic energy of particles

Kelvin = Kelvin = ooC + 273C + 273

Inc. Temp. = Inc. EnergyInc. Temp. = Inc. Energy

Dec. Temp = Dec. EnergyDec. Temp = Dec. Energy

Kinetic-Molecular TheoryKinetic-Molecular Theory

Assumptions for Assumptions for IDEAL GASESIDEAL GASES (imaginary gases)(imaginary gases)

Particles = 0 volumeParticles = 0 volume No attraction between particlesNo attraction between particles

Real gases HAVE volume and SOME Real gases HAVE volume and SOME attraction b/ particlesattraction b/ particles

Properties of GasesProperties of GasesExpansion – Expansion – constant, random motionconstant, random motion

Fluidity – Fluidity – low attractionlow attraction

Low densityLow density – particles far apart – particles far apart

Compressibility – Compressibility – easily change pressure easily change pressure and volumeand volume

Diffusion –Diffusion – gases mix easily gases mix easily

EffusionEffusion – pass through tiny openings – pass through tiny openings

Measuring GasesMeasuring Gases

Measuring GasesMeasuring Gases

Pressure depends on temp. and volumePressure depends on temp. and volume Def:Def: force per unit of area force per unit of area Many units pg. 364Many units pg. 364

1 atm = 760 mmHg = 760 torr = 1 atm = 760 mmHg = 760 torr =

14.70 psi = 101,325 Pa = 101.325 kPa14.70 psi = 101,325 Pa = 101.325 kPa

BarometerBarometer – device used to measure – device used to measure atmospheric pressure (p. 363)atmospheric pressure (p. 363)

ExamplesExamples

15.0 psi = ? atm15.0 psi = ? atm

693 mmHg = ? Pascals693 mmHg = ? Pascals

Dalton’s Law of Partial Dalton’s Law of Partial PressurePressure

Gas MIXTURESGas MIXTURES

Each gas has Each gas has partial pressurepartial pressure

Dalton’s Law states:Dalton’s Law states:

The sum of the partial pressures of The sum of the partial pressures of all the gases in the mixture is equal all the gases in the mixture is equal to the total pressure of the mixture.to the total pressure of the mixture.

PPTT = p = paa + p + pbb + p + pcc + … + …

Dalton’s LawDalton’s Law

If the atmospheric pressure is 767 mmHg If the atmospheric pressure is 767 mmHg and the partial pressures of nitrogen and and the partial pressures of nitrogen and oxygen are 604 mmHg and 162 mmHg, oxygen are 604 mmHg and 162 mmHg, what is the partial pressure of argon?what is the partial pressure of argon?

Dalton’s LawDalton’s Law

What is the partial pressure of nitrogen in What is the partial pressure of nitrogen in air if the total pressure is 1.5 atm and air if the total pressure is 1.5 atm and nitrogen makes up 15% of the air?nitrogen makes up 15% of the air?

Dalton’s Law over WaterDalton’s Law over Water

p. 366p. 366

Gases are then mixed with HGases are then mixed with H22O vaporO vapor

PPatmatm = P = Pgasgas + P + Pwaterwater

PPwaterwater varies with temp. (p. 859) varies with temp. (p. 859)

Sample of NSample of N22 gas was collected over water gas was collected over water

at 23.0at 23.0ooC. What is the pressure of the NC. What is the pressure of the N22

if the atmospheric pressure is 785 mmHg?if the atmospheric pressure is 785 mmHg?

Boyle’s LawBoyle’s Law

Boyle’s LawBoyle’s Law

Pressure – Volume RelationshipPressure – Volume Relationship P and V are P and V are inversely proportional inversely proportional at constant at constant

temperature. temperature.

As one As one the other the other ..

Boyle’s LawBoyle’s Law

PPooVVoo = P = PnnVVnn

PPoo = original Pressure = original Pressure

VVoo = original Volume = original Volume

PPnn = new Pressure = new Pressure

VVnn = new Volume = new Volume

Boyle’s LawBoyle’s Law

A gas at 25A gas at 25ooC and 748 mmHg occupies C and 748 mmHg occupies 2.18 L. At 252.18 L. At 25ooC, what is the pressure, in C, what is the pressure, in Pa, if you decreased the volume to 0.541 Pa, if you decreased the volume to 0.541 L?L?

Boyle’s LawBoyle’s Law

A gas has a volume of 0.923 L at 23A gas has a volume of 0.923 L at 23ooC C and 1.00 atm. What is the volume if you and 1.00 atm. What is the volume if you increased the pressure to 946 torr at increased the pressure to 946 torr at 2323ooC?C?

Charles’s LawCharles’s Law

Charles’s LawCharles’s Law

Volume – Temperature RelationshipVolume – Temperature Relationship V and T are V and T are directly proportionaldirectly proportional at constant at constant

pressurepressure As one As one the other the other T is in KELVIN!!T is in KELVIN!!

Charles’s LawCharles’s Law

VVoo = = VVnn

TToo T Tnn

VVoo = original Volume = original Volume

TToo = original Temperature = original Temperature

VVnn = new Volume = new Volume

TTnn = new Temperature = new Temperature

Charles’s LawCharles’s Law

A sample of gas at a constant pressure A sample of gas at a constant pressure and –18and –18ooC has a volume of 1.00L. What is C has a volume of 1.00L. What is the temperature if the volume is changed the temperature if the volume is changed to .45L?to .45L?

Gay-Lussac’sGay-Lussac’s

Gay-Lussac’sGay-Lussac’s

Pressure – Temperature RelationshipPressure – Temperature Relationship P and T are P and T are directly proportionaldirectly proportional at constant at constant

volumevolume As one As one the other the other T is in KELVIN!!T is in KELVIN!!

Combined Gas LawCombined Gas Law

At 15At 15ooC a gas occupies .59 L at a pressure C a gas occupies .59 L at a pressure of 23 psi. What is the temperature if the of 23 psi. What is the temperature if the volume was increased to 1.09 L and the volume was increased to 1.09 L and the pressure was 1.2 atm?pressure was 1.2 atm?

Combined Gas LawCombined Gas Law

A gas cylinder at 20.0A gas cylinder at 20.0ooC is thrown into an C is thrown into an incinerator where the temperature is incinerator where the temperature is 500.0500.0ooC. If the pressure was initially 1.0 C. If the pressure was initially 1.0 atm, what pressure did it reach inside the atm, what pressure did it reach inside the incinerator? (assuming at constant V and incinerator? (assuming at constant V and did not explode)did not explode)

Avogadro’s LawAvogadro’s Law

Avogadro’s LawAvogadro’s Law

Def:Def: equal volumes of gases at same T equal volumes of gases at same T and P contain equal # of moleculesand P contain equal # of molecules All gas particles so small ~ same sizeAll gas particles so small ~ same size

STPSTP : Standard Temperature & Pressure : Standard Temperature & Pressure 00ooC and 1 atmC and 1 atm At STP, At STP, 1 mole = 22.4 L1 mole = 22.4 L

Gas StoichiometryGas Stoichiometry

What What volumevolume of H of H22 gas is produced from gas is produced from

3.9 g of NH3.9 g of NH33, at STP?, at STP? Need mol HNeed mol H22 L H L H22 gas gas

2NH2NH33(g) (g) 3H 3H22(g) + N(g) + N22(g)(g)

Gas StoichiometryGas Stoichiometry

Xenon gas reacts w/ excess fluorine gas Xenon gas reacts w/ excess fluorine gas to produce Xenon hexafluoride. Need to to produce Xenon hexafluoride. Need to produce 3.14 L XeFproduce 3.14 L XeF66, how many L of , how many L of

fluorine do we need?fluorine do we need? Use Mole Ratios as VOLUME ratiosUse Mole Ratios as VOLUME ratios

Ideal Gas LawIdeal Gas Law

Ideal Gas LawIdeal Gas LawGive “instant” resultsGive “instant” results

Compares: P, V, T and n (moles) of Compares: P, V, T and n (moles) of ideal gasesideal gases

At normal conditions real gases ARE At normal conditions real gases ARE ideal gasesideal gases

At LOW temp. and HIGH pressure real At LOW temp. and HIGH pressure real gases ARE NOT ideal gasesgases ARE NOT ideal gases

Ideal Gas LawIdeal Gas Law

PV = nRTPV = nRT

P = pressure in P = pressure in atmatm

V = volume in V = volume in LL

n = molesn = moles

T = temp. in KELVIN!!T = temp. in KELVIN!!

R = R = ideal gas constantideal gas constant

0.0821 L atm/ mol K0.0821 L atm/ mol K

ExamplesExamples

How many moles of gas at 100.How many moles of gas at 100.ooC does it C does it take to fill a 1.00 L flask to a pressure of take to fill a 1.00 L flask to a pressure of 22.1 psi?22.1 psi?

ExamplesExamples

What is the volume occupied by 9.45 g of What is the volume occupied by 9.45 g of CC22HH22 at STP? at STP?