Presentation on theme: "I. Kinetic Molecular Theory KMT. Assumptions of KMT All matter is composed of tiny particles These particles are in constant, random motion. Some particles."— Presentation transcript:
I. Kinetic Molecular Theory KMT
Assumptions of KMT All matter is composed of tiny particles These particles are in constant, random motion. Some particles are moving fast, some are moving slowly. Temperature is a measure of the average Kinetic Energy and is proportional to the average speed of the molecules.
KMT Model op_KMT_frames.htm op_KMT_frames.htm Click on the link above to see how particles of matter behave according to the KMT.
Liquids & Solids II. Intermolecular Forces
Definition of IMF Attractive forces between molecules. Much weaker than chemical bonds within molecules. a.k.a. van der Waals forces
Types of IMF London Dispersion Forces View animation online.animation
Types of IMF Dipole-Dipole Forces + + - - View animation online.animation
Types of IMF Hydrogen Bonding
Types of IMF
III. Physical Properties Liquids & Solids
Liquids vs. Solids LIQUIDS Stronger than in gases Y high N slower than in gases SOLIDS Very strong N high N extremely slow IMF Strength Fluid Density Compressible Diffusion
Liquid Properties Surface Tension attractive force between particles in a liquid that minimizes surface area
Liquid Properties Capillary Action attractive force between the surface of a liquid and the surface of a solid watermercury
Melting Amount of energy needed to melt a substance depends on forces keeping particles together. Melting water requires a high amount of energy because of hydrogen bonding Adding energy allows molecules to move faster, breaking the hydrogen bonds Melting point - Temperature at which the forces holding crystal lattice together are broken and substance becomes liquid
Which has a higher m.p.? polar or nonpolar? covalent or ionic? Phase Changes Melting Point equal to freezing point polar ionic IMFm.p.
Vaporization In liquid water, some particles will have more kinetic energy than others. When the particles have enough energy to overcome the forces of attraction they will escape the liquid as a gas. Vapor - A substance that is liquid at room temperature and becomes gas. Vaporization - the process of changing a liquid to a gas
Vaporization Evaporation - Vaporization that occurs at the surface of a liquid, molecules at the surface gain enough energy to overcome IMF Evaporation is gradual Even at cold temperatures, some molecules have enough energy to break the attractions and become gas. Evaporation is how your body cools itself Water in sweat absorbs heat from your body Water evaporates leaving less heat in your body and a lower ‘average kinetic energy’ (lower temperature)
Phase Changes Vapor Pressure pressure of vapor above a liquid at equilibrium IMFv.p.tempv.p. depends on temp & IMF p.478 temp v.p.
Phase Changes Boiling Point IMFb.p.P atm b.p. Temperature at which the vapor pressure of a liquid equals the external atmospheric pressure depends on P atm & IMF Normal B.P. - b.p. at 1 atm
Sublimation Sublimation - when a substance goes from solid directly to gas without becoming a liquid Solid iodine Frozen carbon dioxide (dry ice) Moth balls (p-dichlorobenzene) Solid air fresheners Ice cubes left in a freezer for a long time
Phase Changes the Release Energy Condensation Deposition Freezing
Condensation Condensation – process of changing from gas to liquid When molecule s lose energy, Velocity of the molecules is reduced Intermolecular forces take over Hydrogen bonds form, energy is released (heat comes out) There are different causes for condensation, however, all involve loss of energy: Contact with cold item
Phase Changes Equilibrium trapped molecules reach a balance between evaporation & condensation
Deposition Deposition – changing from gas directly to solid Snowflakes
Freezing Freezing – process of changing from liquid to solid Remove energy from liquid Molecules don’t move past each other any longer Molecules stay in fixed, set position Become solid
Phase Changes Energy RequiredEnergy Released Solid Liquid Melting or fusion Liquid Solid freezing Liquid Gas Vaporization, evaporation or boiling Gas Liquid condensation Solid Gas sublimation Gas Solid solidification
Phase Diagrams Phase diagram shows phase of matter at different temperatures and pressures Each substance is unique X-axis usually temperature Y-axis usually pressure There is usually a “Triple Point” where all three phases can coexist “ Critical Point” – temperature and pressure above which substance cannot exist as liquid
Phase Diagram - Water
Phase Diagram CO 2
Heating Curves Kinetic Energy Changes – Heat Energy speeds up the molecules. Potential Energy Changes – Heat energy separates the molecules from solid to liquid, liquid to gas.
Heating Curves Temperature Change change in KE (molecular motion) depends on heat capacity Heat Capacity energy required to raise the temp of 1 gram of a substance by 1°C
Phase Change The energy involved in a phase change is calculated using: Heat of Fusion ( H fus ) Heat of Vaporization ( H vap )
Heat of Fusion Heat of Fusion is the energy required to change 1 gram of a substance from the solid to the liquid state without changing its temperature. Heat of Fusion is used for calculations involving the phase changes of solid liquid or liquid solid
Heat of Vaporization Heat of Vaporization ( H vap ) energy required to boil 1 gram of a substance at its b.p. EX: sweating, steam burns, the drinking bird