1. Gases Ch 12

2. 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

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

4. 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

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

6. 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 + P
and using the combined gas law,
EOS
Chapter 5: Gases

7. Partial Pressures Illustrated
PH PHe = Ptotal
EOS
Chapter 5: Gases

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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