1. Kinetic Molecular Theory 1.Based on the idea that particles are always in motion. 2.Explains the properties of solids, liquids, and gases.

2. KMT Accounts for the Physical Properties of Gases Physical Properties of Gases?  Expansion: Gases expand to fill their volume.  Fluidity: Gas particles glide easily past each other.  Low Density: 1/1000 of a solid or liquid.  Compressibility: Volume of a gas can be decreased.  Diffusion: the mixing of particles of 2 substances by random motion; causes gas particles to spread out.  Effusion: Gas particles passing through a tiny opening. Ex: air escaping a balloon through a pinhole.

3. Kinetic Molecular Theory of Gases 1) Helps us to understand the behavior of gases and provides a model of an ideal gas. 2) 5 Assumptions: What are some assumptions we make about gases? a)Gases consist of large numbers of tiny particles that are far apart. b)Collisions between gas particles or with the container walls are ELASTIC (No net loss of Kinetic Energy). c)Gas particles are in constant motion and possess Kinetic Energy (Energy of motion) d)There are no forces of attraction or repulsion between gas particles. e)Average K.E. depends on the temperature of the gas: KE = ½ mv 2.

4. The Real World: Deviations from Ideal Behavior Real Gases  Real gases do not behave according to the assumptions of KMT.  Particles of real gases occupy space and are attracted to each other.  These attractions are considerable at HIGH pressures and LOW temperatures. WHY?  KMT holds true for those gases with little attractions for each other. Ex: He, N 2

5. Variables Needed to Describe a Gas Volume Temperature Pressure = Force/Area  Gas molecules exert pressure on surfaces they collide with.  Atmosphere exerts pressure on objects due to the weight of gases composing it.  Barometers measure atmospheric pressure

6. Barometer

7. Units of Pressure UnitsSymbolDefinition Millimeters of mercury mmHgPressure of that supports 1mm of Hg in a barometer Torricellitorr1 torr = 1 mmHg AtmosphereatmAverage atmospheric pressure at sea level at 0°C PascalPaSI Unit for Pressure 1 Pa = 1N/m 2

8. Pressure Conversions Convert 550. torr into atmospheres of pressure (atms) 550. torr x 1.00 atm = 760. torr 0.724 atm

9. Dalton’s Law of Partial Pressures The total pressure of the mixture of gases is equal to the sum of the partial pressures of each individual gas. Expressed as P TOTAL = P 1 + P 2 + P 3 + … Explain in terms of Kinetic Molecular Theory.

10. Applications of Partial Pressure Calculate the partial pressure in mmHg of the 4 main gases of air at 760 mmHg. Their abundance by volume are: N 2 = 78.08%, O 2 = 20.95%, Ar = 0.934% CO 2 = 0.035% N2:N2: 78.08 = x 100 760 mmHg

11. Gases Collected by Water Displacement Gases collected by water displacement are mixed with water vapor. P atm = P gas + P water

12. Volume-Mass Relationships of Gases 1. Gay-Lussac: a) Studies gas volume relationships. Hydrogen gas + Oxygen gas  Water Vapor 2 Liters 1 Liter  2 Liters b) Law of Combining Volumes of gases (1808): At constant temperature and pressure, the volumes of gases can be expressed as small whole number ratios. c) Observations don’t fit with parts of Dalton’s Atomic Theory.

13. Avogadro explains G-L Combining Volumes without violating Dalton’s Atomic Theory! 1. Avogadro (1811): a) Molecules can contain more than 1 atom. b) Avogadro’s Law: At the same T and P, EQUAL volumes of gases contain EQUAL numbers of molecules. 2H 2 + O 2  2H 2 O 2 L 1L  2L 2 Molecules 1 molecule 2 molecules

14. In Summary…Avogadro’s Law 1.Diatomic molecules exist 2.Gas VOLUME is directly proportional to the AMOUNT of gas (n). (V~ n) 3.Equal VOLUMES of gases contain equal NUMBER OF PARTICLES.

15. Effusion and Diffusion 1.Diffusion: Mixing of 2 gases due to their random motion. 2.Effusion: a) Confined gas molecules randomly pass through a tiny opening in a container. b) Can be used to estimate a gas’ molar mass.

16. Rates of Effusion/Diffusion Depends on the velocity of gas molecules, which vary with mass. Graham’s Law of Effusion: Rates of effusion/diffusion are inversely proportional to molar masses.

18. The Molar Relationship Involving Mass and Volume Objectives: Determine the mass of a piece of Mg ribbon (calculation – I will give you the mass of a 1.000m piece of Mg.) React the Mg with HCl (aq) and collect the gaseous product. (Write a balanced equation for the reaction.) Measure the volume of the gas collected AFTER equalizing the pressure AND convert what the volume would be at STP. Calculate the molar relationship between the Mg consumed and the gas produced.