CHAPTER 5CHAPTER 5

AP CHEMISTRYAP CHEMISTRY

PRESSUREPRESSURE BarometerBarometer

– Measure the Measure the atmospheric pressureatmospheric pressure

Atmospheric pressureAtmospheric pressure– Mass of the air being Mass of the air being

pulled toward the pulled toward the center of the earth by center of the earth by gravitygravity

– Manometer - on the Manometer - on the boardboard

– 1 standard atm. = 760 1 standard atm. = 760 mmHg = 760 torr = mmHg = 760 torr = 101.325 kPa101.325 kPa

Gas lawsGas laws– Boyles lawBoyles law– PP11VV11 = P = P22VV22

A gas that obeys the gas laws A gas that obeys the gas laws (look law up in book) is an (look law up in book) is an Ideal Ideal GasGas– Charles's lawCharles's law– VV11 = = VV22

TT11 T T22

A gas cannot have a negative A gas cannot have a negative volume. Therefore, temperature volume. Therefore, temperature can never be below 0K. 0K will can never be below 0K. 0K will never be reached. Closest is never be reached. Closest is 0.000001 K0.000001 K

CONTINUEDCONTINUED Avogardro’s lawAvogardro’s law

– Volume is directly proportional to the number of molesVolume is directly proportional to the number of moles– VV11 = = VV22

nn11 n n22

Ideal gas lawIdeal gas law– PV = nRT PV = nRT – R = 0.08206 LR = 0.08206 L..atm/ Katm/ K..molmol

Combined gas lawCombined gas law– PP11VV11 = = PP22VV22

TT11 T T2 2

MOLAR MASS OF GASMOLAR MASS OF GAS Molar mass (MM) = Molar mass (MM) = dRTdRT PP

– d = densityd = density Partial pressurePartial pressure Total pressure exerted is the sum of ALL Total pressure exerted is the sum of ALL

gas pressures gas pressures PPtotaltotal = P = P11 + P + P22 + ........ + ........ = n= ntotaltotal(RT/V)(RT/V)

MOLE FRACTIONMOLE FRACTION Ratio of the number of moles to the total number Ratio of the number of moles to the total number

of molesof moles XX11 = n = n11/n/ntotaltotal = P = P11/P/Ptotaltotal If a gas is collected by displacing water then the If a gas is collected by displacing water then the

gas obtained would be a mixture of the gas and gas obtained would be a mixture of the gas and water vapor. The water vapor pressure would water vapor. The water vapor pressure would need to be removed before you could use the need to be removed before you could use the gases pressure.gases pressure.

Find the water vapor pressure at the temperature Find the water vapor pressure at the temperature given and subtract it from the total pressuregiven and subtract it from the total pressure

KINETIC THEORY OF GASESKINETIC THEORY OF GASES The volume of individual particles are assumed zeroThe volume of individual particles are assumed zero Particles are in constant motionParticles are in constant motion Particles exert no force on each otherParticles exert no force on each other Average kinetic energy is directly proportional to its Kelvin Average kinetic energy is directly proportional to its Kelvin

temperaturetemperature Real Gases have finite volumes and do exert forces on each Real Gases have finite volumes and do exert forces on each

otherother (KE)(KE)averageaverage = 3/2 RT = 3/2 RT Kelvin temperature is an index of the random motions of the Kelvin temperature is an index of the random motions of the

particles of gasesparticles of gases Root mean square velocity (special kind of average)Root mean square velocity (special kind of average) UUrms rms = (3RT/M)= (3RT/M)1/21/2

U = m/s, R = 8.3145 J/KU = m/s, R = 8.3145 J/K..mol, J = kgmol, J = kg..mm22/s/s22, M = kg/mol, M = kg/mol

EFFUSION AND DIFFUSIONEFFUSION AND DIFFUSIONREAL GASESREAL GASES

Effusion Effusion – Passage of a gas through a tiny orifice into a evacuated Passage of a gas through a tiny orifice into a evacuated

chamberchamber– Rate of effusion for gas 1Rate of effusion for gas 1 = = UUrmsrmsXX11 = (M = (M22))1/21/2

Rate of effusion for gas 2 URate of effusion for gas 2 Urmsrms X X22 (M (M11))1/21/2 – Molar mass (g/mol) is M in this formulaMolar mass (g/mol) is M in this formula

DiffusionDiffusion– Mixing of gasesMixing of gases

Real gasesReal gases– Ideal gas behavior only occurs for real gases under the Ideal gas behavior only occurs for real gases under the

following conditionsfollowing conditions– Low pressure and/or high temperatureLow pressure and/or high temperature

CONTINUEDCONTINUED

Van der Waal equationVan der Waal equation– [P[Pobsobs + a(n/V) + a(n/V)22] x (V - nb) = nRT] x (V - nb) = nRT– PPobsobs = observed pressure, = observed pressure, a(n/V)a(n/V)22 = pressure correction, = pressure correction, (V - nb) = corrected volume(V - nb) = corrected volume– A and b are varied until the best fit of the A and b are varied until the best fit of the

observed pressure is obtained. These are observed pressure is obtained. These are found on table 5.3found on table 5.3

Read 5.10 UNDERSTAND THIS SECTIONRead 5.10 UNDERSTAND THIS SECTION