Gases Ch 12

Avogadro’s Law: Mole-Volume Relationship At a fixed temperature and pressure, the volume of a gas is directly proportional to the amount of gas in moles (n) or to the number of molecules of gas EOS

The Ideal Gas Law The constant of proportionality (k) is given the symbol R R = 8. 314 kPa  L atm  mol–1  K–1 EOS

Units for the Gas Constant, R EOS All units are “energy per mol per Kelvin” Joules (J) is the energy unit most frequently encountered Chapter 5: Gases

Molecular Mass Determination The molar mass of a gas can be determined using the ideal gas law EOS PV = nRT becomes

Dalton’s Law of Partial Pressure The total pressure exerted by a mixture of gases is equal to the sum of the partial pressures exerted by the separate gases Ptotal = P1 + P2 + P3 + ... and using the combined gas law, EOS Chapter 5: Gases

Partial Pressures Illustrated PH2 + PHe = Ptotal EOS Chapter 5: Gases

Mole Fraction The partial pressure is the product of mole fraction times total pressure P1 = x1 . Ptotal The composition of gaseous mixtures is often given in percent by volume and this is equal to mole percent EOS Chapter 5: Gases

Gay-Lussac’s Law of Combining Volumes For the reaction: 2 H2(g) + O2(g)  2 H2O(g) the ratio is 2:1:2 EOS

The Law of Combining Volumes When gases measured at the same temperature and pressure are allowed to react, the volumes of gaseous reactants and products are in small whole-number ratios EOS Relates volumes of any two gaseous species in a reaction, even if some reactants or products are liquid or solid

Ideal Gas Equation In Reaction Stoichiometry Ratios of gas volumes can be substituted for mole ratios only for gases and only if the gases are at the same temperature and pressure Often the amount of a gaseous reactant or product needs to be related to that of a solid or liquid EOS The ideal gas equation allows us to relate mole of gas to other gas properties Chapter 5: Gases

Summary of Concepts Gases consist of widely separated molecules that are moving constantly and randomly throughout the container Molecular collisions with containers give rise to pressure EOS Chapter 5: Gases

Summary of Concepts The ideal gas equation can be used in place of the simple or combined gas laws, especially in molecular mass and gas density determinations, and in stoichiometric calculations for reactions involving gases EOS The total pressure of a gaseous mixture is the sum of the partial pressures of each gas Chapter 5: Gases

Summary of Concepts The kinetic-molecular theory provides a basis for describing the diffusion and effusion of gases EOS Real gases are more likely to exhibit ideal behavior at high temperatures and low pressures Chapter 5: Gases