The Kinetic-Molecular The Kinetic-Molecular Theory of MatterTheory of Matter

Objective 2.05Objective 2.05

Ideal GasesIdeal Gases

►An An imaginaryimaginary gas that perfectly fits all gas that perfectly fits all the assumptions about kinetic the assumptions about kinetic molecular theorymolecular theory

►Kinetic Molecular Theory of Gases Kinetic Molecular Theory of Gases (KMT)(KMT) explains the properties of gasesexplains the properties of gases

Kinetic-Molecular Theory of Kinetic-Molecular Theory of GasesGases

►Assumptions about Ideal GasesAssumptions about Ideal Gases particles are spread far apartparticles are spread far apart mostly empty spacemostly empty space Collisions are elastic collisions Collisions are elastic collisions Particles are in continuous, random Particles are in continuous, random

motionmotion no forces of attraction or repulsion no forces of attraction or repulsion average kinetic-energy = temperatureaverage kinetic-energy = temperature

However…….However…….

►Real Gases Real Gases Do not follow KMT completelyDo not follow KMT completely But we can use the KMT to describe themBut we can use the KMT to describe them How they differ:How they differ:

►Occupy spaceOccupy space►Particles ARE attracted to each other (to some Particles ARE attracted to each other (to some

degree)degree)►Nonpolar gases deviate less than polar gasesNonpolar gases deviate less than polar gases

Nature of gases explained by Nature of gases explained by KMTKMT

► ExpansionExpansion► FluidityFluidity► Low DensityLow Density► CompressibilityCompressibility►Diffusion Diffusion

Units of pressureUnits of pressure

►Mm of HgMm of Hg►TorrTorr►Atmospheres (atm)Atmospheres (atm)►Kilopascals (kPa)Kilopascals (kPa)

►Pressure Unit ConversionsPressure Unit Conversions 1 atm = 760 mmHg = 760 torr = 101.3 1 atm = 760 mmHg = 760 torr = 101.3

kPakPa

Units of TemperatureUnits of Temperature

►Celsius (˚C)Celsius (˚C)►Kelvin (K)Kelvin (K)

K = ˚C + 273K = ˚C + 273

Standard temperature and Standard temperature and pressurepressure

(STP)(STP)►1 atm…OR1 atm…OR

760 mm Hg760 mm Hg 760 torr760 torr 101.3 kPa101.3 kPa

►273 K (0273 K (0° C)° C)

The Gas LawsThe Gas Laws

►Combined Gas LawCombined Gas Law

PP11VV1 1 = P= P22VV22

TT11 T T22

Used to determine pressure, Used to determine pressure, temperature or volume of a gas temperature or volume of a gas

Examples of Gas Problems using Examples of Gas Problems using Combined Gas LawCombined Gas Law

►Pg. 315 Sample Problem 10-2Pg. 315 Sample Problem 10-2►Pg. 318 Sample Problem 10-3Pg. 318 Sample Problem 10-3►Pg. 320 Sample Problem 10-4Pg. 320 Sample Problem 10-4►Pg. 321 Sample Problem 10-5Pg. 321 Sample Problem 10-5

►Remember T must be in Kelvin!Remember T must be in Kelvin!►Remember P units must be all the same!Remember P units must be all the same!►Whichever unit is constant cancels out!!!Whichever unit is constant cancels out!!!

The Gas LawsThe Gas Laws

►Boyles Law:Boyles Law:

►Charles Law: Charles Law:

►Gay Lussac’s LawGay Lussac’s Law

Ideal Gas LawIdeal Gas Law

►Mathematical relationship among Mathematical relationship among pressure, volume, temperature, and pressure, volume, temperature, and the the number of molesnumber of moles of a gas of a gas

►PV=nRTPV=nRT (given on Reference Guide)(given on Reference Guide)

Pressure (P)Pressure (P) Volume (V)Volume (V) Number of moles (n)Number of moles (n) Ideal gas constant (get from table on Ideal gas constant (get from table on

sheets)sheets) Temperature (T) Temperature (T)

Examples of Ideal Gas Examples of Ideal Gas ProblemsProblems

►Pg. 342 Sample Problem 11-3Pg. 342 Sample Problem 11-3►Pg. 343 Sample Problem 11-4Pg. 343 Sample Problem 11-4►Pg. 344 Sample Problems 11-5Pg. 344 Sample Problems 11-5

Dalton’s Law of Partial Dalton’s Law of Partial PressuresPressures

►The total pressure of a mixture of The total pressure of a mixture of gases is equal to the sum of the partial gases is equal to the sum of the partial pressures of the component gasespressures of the component gases

►PPTT=P=P11+P+P22+P+P33+… +… (given on reference guide)(given on reference guide)

►Also…for gas collected over waterAlso…for gas collected over water PPT T = P= Pgasgas + P + PH2OH2O

Example of Partial Pressures Example of Partial Pressures ProblemProblem

►Pg. 324 Sample Problem 10-6Pg. 324 Sample Problem 10-6

►To get water pressure use To get water pressure use ►Water Vapor Pressure Table Appendix A pg Water Vapor Pressure Table Appendix A pg

899899

Avogadro’s Law for GasesAvogadro’s Law for Gases

►Gases of the same volume, at the Gases of the same volume, at the same temp and pressure, have the same temp and pressure, have the same number of molecules!same number of molecules!

►n/V = n/Vn/V = n/V►A mole ratio in an equation can A mole ratio in an equation can

become a VOLUME ratio when all become a VOLUME ratio when all compounds are gasescompounds are gases

Example of Avogadro’s LawExample of Avogadro’s Law

HH22 (g)(g) + Cl + Cl22 (g)(g) 2HCl 2HCl (g)(g)

Mole Ratio: 1 mol:1mol:2molMole Ratio: 1 mol:1mol:2mol

Volume Ratio: 1L : 1L :2LVolume Ratio: 1L : 1L :2L

Molar Volume of A GasMolar Volume of A Gas

►At STPAt STP

1 mole of any gas = 22.4 L1 mole of any gas = 22.4 L

New Branch on Mole MapNew Branch on Mole Map