States of Matter

1. States of Matter 13.1 The Nature of Gases 13.2 The Nature of Liquids 13.3 The Nature of Solids 13.4 Changes of State Created by C. Ippolito June 2007

2. The Nature of Gases Objectives Describe the assumptions of the kinetic theory as it applies to gases Interpret gas pressure in terms of kinetic theory Define the relationship between Kelvin temperature and average kinetic energy Created by C. Ippolito June 2007

3. Kinetic Theory & a Model for Gases • Kinetic Energy • energy an object has because of its motion • Kinetic Theory • all matter consists of tiny particles in constant motion • Gas Particles • small, hard spheres of insignificant volume • motion is rapid, constant, and random • collisions are perfectly elastic Created by C. Ippolito June 2007

4. Gas Pressure • result of force exerted by gas per unit surface area of an object • from simultaneous collisions of billions of rapidly moving particles in an object • Vacuum • an empty space with no particles and no pressure • Atmospheric Pressure • from collisions of atoms and molecules in air • Barometer • measures atmospheric pressure • SI unit is the pascal (Pa) • Standard Atmosphere • pressure to support 760mm of Hg at 25°C 1 atm = 760 mm Hg = 101.3 kPa Created by C. Ippolito June 2007

5. Converting Between Units of Pressure Created by C. Ippolito June 2007

6. Kinetic Energy and Temperature • Average kinetic energy and temperature are related •  kinetic energy  temperature •  kinetic energy  temperature • Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of a substance Created by C. Ippolito June 2007

7. The Nature of Liquids Objectives Identify factors that determine physical properties of a liquid Define evaporation in terms of kinetic energy Describe equilibrium between a liquid and its vapor. Identify the conditions at which boiling occurs Created by C. Ippolito June 2007

8. Model for Liquid • Intermolecular forces of attraction keep liquid particles close together • interplay between disruptive particles in a liquid and the attraction of particles determine the physical properties of liquids • Liquid particles are • closer together than gases • more dense than gases • little affected by pressure Created by C. Ippolito June 2007

9. Evaporation • Vaporization • conversion of a liquid into a gas • Evaporation • process by particles at surface of liquid converts to gas without boiling • only molecules with a certain minimum kinetic energy can escape from surface of liquid Created by C. Ippolito June 2007

10. Vapor Pressure • measure of the force exerted by a gas above a liquid • at constant vapor pressure, a dynamic equilibrium exists between the vapor and liquid. • rate of evaporation = rate of condensation •  temperature  vapor pressure Created by C. Ippolito June 2007

11. Vapor Pressure Measurement • Manometer • measures vapor pressure Created by C. Ippolito June 2007

12. Boiling Point • A liquid begins to boil, when heated to a temperature at which all of its particles have enough kinetic energy to vaporize • Boiling Point • temperature where • vapor pressure of liquid = external pressure on liquid Created by C. Ippolito June 2007

13. Boiling Point and Pressure Changes Created by C. Ippolito June 2007

14. Normal Boiling Point • boiling point at 1 atm or 101.3 kPa Created by C. Ippolito June 2007

15. The Nature of Solids Objectives Evaluate how the way particles are organized explains the properties of solids Identify the factors that determine the shape of a crystal Explain how allotropes of an element are different Created by C. Ippolito June 2007

16. Model for Solids • General properties of solids reflect an orderly arrangement of particles and the fixed location of particles • Melting Point • temperature at which a solid changes into a liquid Created by C. Ippolito June 2007

17. Crystal Structure & Unit Cells • shape of a crystal reflects the arrangement of the particles • Crystal Systems • Seven Systems • Cubic, Tetragonal, Orthorhombic, Monoclinic, Triclinic, Hexagonal, Rhombohedral • characterized in terms of • angles between faces (α, β, γ) • length of edges on each face (a, b, c) • Unit Cell • smallest group of particles that retain geometric shape of the crystal • Simple Cubic • Body Centered • Face Centered Created by C. Ippolito June 2007

18. Allotropes • two or more different molecular forms of the same element in the same physical state • different properties • different structures • Carbon (diamond, graphite, fullerenes) Created by C. Ippolito June 2007

19. Changes of State Objectives Identify the conditions necessary for sublimation Describe how equilibrium conditions are represented in a phase diagram Created by C. Ippolito June 2007

20. Sublimation • change of a substance from a solid to a vapor without passing through the liquid state • occurs in solids with vapor pressures that exceed atmospheric temperature at or near room temperature Created by C. Ippolito June 2007

21. Phase Diagrams • A graphic representation of the relationships among solid, liquid, and vapor states in a sealed container • pressure and temperature at which two phases exist in equilibrium are indicated by a line separating the phases • triple point • the only set of conditions at which all three phases can exist at equilibrium Created by C. Ippolito June 2007