Gases and the Kinetic Molecular Theory Principles of General Chemistry, 2nded. By M. Silberberg Chemistry, 8th ed.by W. Whitten, R. Davis, R., M. L. Peck, and G. Stanley. 2 Chapter Goals 1.Comparison of Solids, Liquids, and Gases 2.Pressure 3.The Kinetic-Molecular Theory 4.Boyle’s Law: The Volume-Pressure Relationship 5.Charles’ Law: The Volume-Temperature Relationship; The Absolute Temperature Scale 6.Standard Temperature and Pressure 7.The Combined Gas Law Equation 8.Avogadro’s Law and the Standard Molar Volume3 Chapter Goals 9.Summary of Gas Laws: The Ideal Gas Equation 10.Determination of Molecular Weights and Molecular Formulas of Gaseous Substances 11.Dalton’s Law of Partial Pressures12.Mass-Volume Relationships in Reactions Involving Gases 13.Diffusion and Effusion of Gases 14.Real Gases: Deviations from Ideality 4 The Distinction of Gases from Solids and Liquids 1. Gas volume changes greatly with pressure. 2. Gas volume changes greatly with temperature. 3. Gases have relatively low viscosity. 4. Most gases have relatively low densities under normal conditions. 5. Gases are miscible, i.e. gases always form homogeneous mixtures with other gases. 5 6 •the force acting on an object per unit area Pressure
7 •Atmospheric pressure is measured using a barometer. = 1 atm = 76 cmHg = 760 mmHg = 760 torr = 101.3 kPa Pressure 8 The Kinetic-Molecular Theory •Postulate 1 –Gases consist of discrete molecules that are relatively far apart and have few intermolecular attractions. –The volume of individual molecules is very small compared to the gas’s volume.•Postulate 2 –Gas molecules are in constant, random, straight line motion with varying velocities. 9 •Postulate 3 –Gas molecules have elastic collisions with themselves and the container, i.e. the total energy is conserved during a collision. The Kinetic-Molecular Theory •Postulate 4 –The kinetic energy of the molecules is proportional to the absolute temperature. –The average kinetic energies of molecules of different gases are equal at a given temperature. 10 Gas Laws - show the relationship between pressure, temperature, volume & number of moles of a sample of gas •Boyle’s Law•Charle’sLaw •Amonton’sLaw •Combined Gas Law •Avogadro’s Law•Ideal Gas Law •Dalton’s Law of Partial Pressures 11 Boyle’s Law: The Volume-Pressure Relationship •at constant temperature, the volume occupied by a fixed amount of gas is inversely proportionalto the applied (external) pressureP ↓, V ↑(at constant temp.) , PV = constant Va1 P P1V1= P2V2constant P , V= 12 Boyle’s Law: The Volume-Pressure Relationship
13 •At 25oC a sample of He has a volume of 400.0 mL under a pressure of 760.0 torr. What volume would it occupy under a pressure of 2.00 atm at the same T?