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Chapter 13 Gases Kinetic-Molecular Theory of Gases.

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Presentation on theme: "Chapter 13 Gases Kinetic-Molecular Theory of Gases."— Presentation transcript:


2 Chapter 13

3 Gases Kinetic-Molecular Theory of Gases

4 §All particles are in constant motion. §As temperature increases kinetic energy ? increases §As gas particles move apart the volume ? increases

5 Point Masses §Gas particles are treated as a point with no volume and no mutual attraction -this is because they’re so small compared to the distances between them.

6 Ideal Gases §A theoretical gas with no volume and no attraction. §A series of theories will be studied about ideal gases -standard pressure of 101.32 kPa -standard temperature of 0°C or 273K -standard conditions are abbreviated STP

7 Therefore: §Kinetic theory explains properties of gases based on a molecular view. §The assumptions are: l The molecules are in continuous, random motion. l A molecule has negligible volume. l The forces between molecules are negligible. l The average kinetic energy depends on the temperature.

8 Four Gas Law Variables Are: §V = volume §P = pressure §T = temperature §n = number of particles §(Upper and Lower Case is important)

9 Behavior of Gases §Compression §Expansion §Diffusion – movement of material from high to low concentration - lighter particles diffuse faster than heavier particles §Effusion- gas escapes through a tiny opening

10 Gas Pressure §Pressure = force/area §Snowshoes in the snow – force is spread out over a larger area §Gas particles exert pressure as they collide with the walls of their container §More particles in a given space, greater pressure §Barometer is tool used to measure atmospheric pressure – mercury rises or falls

11 Units of pressure §SI unit is Pascal (Pa) §1Pa = 1 N/m 2 derived from force §1atm = 760mm Hg = 760 torr = 101.3 kPa =14.7 psi §1torr = 1 mm Hg

12 Dalton’s Law of Partial Pressure §Total pressure of a mixture of gases is equal to the sum of all the pressures of the individual gases §Pg. 392 practice problems

13 Intermolecular Forces (between molecules) §Dispersion Forces – weak forces between temporary dipoles – electron cloud is in constant motion (sometimes called London Forces). §Dipole – Dipole Forces forces between permanent dipoles (polar molecules). §Hydrogen Bonds - a type of dipole-dipole attraction that occurs between molecules containing a hydrogen atom bonded to a small highly electronegative atom (oxygen, nitrogen, or fluorine)

14 Liquids §Denser than gases. §Can’t be easily compressed. §Fluidity – ability to flow (gases and liquids). §Viscosity – measure of the resistance to flow. Decreases with temperature. §Surface Tension – measure of the inward pull by particles in the interior (molecules at the surface have no attractions from above to balance the attractions from below).

15 Liquids (continued) §Capillary Action – liquids in a narrow container form meniscus. This is caused by two forces: l Cohesion – attraction between identical molecules. l Adhesion – attraction between different molecules. l Example – Adhesion between glass and water in a graduated cylinder is greater than cohesion between water molecules. Therefore water rises along the inner walls of the cylinder.

16 Solids §Density is greater than liquids §Crystals – orderly, geometric, 3-D structure. l Atomic l Molecular l Covalent l Ionic l Metallic §Amorphous – not arranged in regular, repeating pattern

17 Phase Changes §That require energy l Melting l Vaporization (Evaporation) l Sublimation §That release energy l Freezing l Condensation l Deposition

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