CHAPTER 12 – GASES AND THE KINETIC-MOLECULAR THEORY1 Comparison of Solids, Liquids, and Gases temperature changes -- have little effect on gases but large effect on liquids and solids pressure changes -- have large effect on gases but little effect on liquidsand solids2 Composition of the Atmosphere and Some Common Properties of Gases gases can be compressed gases exert pressure on their surroundings gases can expand without limit gases diffuse into each other -- i.e., they are miscible (diffuse into each other) gases can be described in terms of their volume (V), temperature (T), pressure (P), and the number of molecules (moles, represented by n) of gas presentn =gMmwhere Mm = molar mass3 Pressure pressure -- force per unit area1 atm = 760 mmHg = 760 torr4 Boyle’s Law: The Pressure-Volume Relationship maintains constant temperature and number of moles volume is inversely proportional to pressureP1Vas one goes up, the other goes down () Boyle’s Law -- assumes number of moles (n) and temperature (T) remain constantP1V1 = P2V25 Charles’ Law: The Volume-Temperature Relationship maintains constant pressure and number of moles volume is directly proportional to the absolute temperature (note that all gas calculations must be done in Kelvin!)V  Tas one goes up, the other goes up as well () Charles’ Law -- assumes number of moles (n) and pressure (P) remain constantV1= V2T T1 26 Standard Temperature and Pressure all gases behave identically at the same temperature and pressure standard pressure -- 1.00000 atm = 760 torr = 760 mmHg standard temperature -- 273.15 K = 0.00 oC other standards -- 1 mol and 22.4 L Gay Lussac’s Law -- assumes number of moles (n) and volume (V) remain constant (note that all gas calculations must be done in Kelvin!)P1=P2T1T27 The Combined Gas Law Equation combines Boyle’s Law, Charles’ Law, and Gay Lussac’s Lawk =PVTif the number of moles of the gas (n) remains constant Combined Gas Law -- assumes number of moles (n) remains constant (note that all gas calculations must be done in Kelvin!)P1V1=P2V2T1T28 Avogadro’s Law and the Standard Molar Volume keep in mind that STP includes 1 mol and 22.4 L maintains constant temperature and pressure volume is directly proportional to number of molesV  n Avogadro’s Law -- assumes temperature (T) and pressure (P) remain constantV1=V2n1n29 Summary of the Gas Laws: The Ideal Gas Equation the ideal gas constant R can have different values due to different unitsR = 8.134 J/mol · KR = 8.134 kg · m2/s2 · K · molR = 1.987 cal/K · mol Ideal Gas Law -- n must be in moles and T must be in Kelvin; all other variables can have any unitsPV = nRT10 Determination of Molecular Weights and Molecular Formulas of Gaseous Substances empirical formula x n = molecular formulawhere n = (molar mass) / (empirical mass)(note that this n is not the same as the n in the previous equations!)11 Dalton’s Law of Partial Pressures Dalton’s Law -- the total pressure exerted by a mixture of ideal gases is the sum of the partial pressures of those gasesPtotal = PA + PB + PC + … mole fraction -- a unitless quantity; essentially a percentage; represented by XAXA=PAPtotalorPA = XA x Ptotal  Raoult’s Law vapor pressure -- a function of temperature; vapor pressure increases astemperature increases (); pressure is the number of collisions that the gas molecules have with the side of the containerso there is more vapor pressure in a sealed container of boiling water (more dots) than there is in a sealed container of ice water (fewer dots)12 Mass-Volume Relationships in Reactions Involving Gases 1 mole of an ideal gas occupies 22.4 liters at standard conditions1 mol = Mm g = 6.022 x 1023 molecules = 22.4 L13 The Kinetic-Molecular Theory gas particles have the same exact velocity before and after colliding with themselves and the sides of the container kinetic energy -- the energy a body possesses by virtue of its motion; the average kinetic energies of different gases are equal at a given temperature (KE  T, where T is absolute temperature)KE = (1/2)(mv2) gas particles move faster at a higher temperature than they do at a lower temperature relating the Kinetic-Molecular Theory to the other gas laws:Boyle’s Law -- P  1/Vas V increases, molecular collisions with container walls decrease and P decreasesDalton’s Law -- Ptotal = PA + PB + PC + …gases have few intermolecular attractions, so their pressures are independent of each otherCharles’ Law -- V  Tan increase in temperature raises the molecular velocities, thus the V increases to keep the P constant14 Diffusion and Effusion of Gasessee lecture outline!15 Deviations from Ideal Gas Behavior real gases behave ideally at ordinary temperatures and pressures; at low temperatures and high pressures, real gases do not behave ideallyFor the Test… be able to name the law and tell how each variable is effected based on various information provided in a question be able to draw intermolecular