2Assumptions 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.
3KMT Model http://preparatorychemistry.com/Bishop_KMT_frames.htm Click on the link above to see how particles of matter behave according to the KMT.
20Phase Changes Each state is referred to as a “Phase” Ice water is a heterogeneous mixture of 2 phasesWhen energy is added or removed, one phase can change into another
21Phase Changes Requiring Energy MeltingVaporizationSublimation
22MeltingAmount of energy needed to melt a substance depends on forces keeping particles together.Melting water requires a high amount of energy because of hydrogen bondingAdding energy allows molecules to move faster, breaking the hydrogen bondsMelting point - Temperature at which the forces holding crystal lattice together are broken and substance becomes liquid
23Phase Changes IMF m.p. Melting Point equal to freezing point Which has a higher m.p.?polar or nonpolar?covalent or ionic?polarionic
24VaporizationIn 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
25VaporizationEvaporation - Vaporization that occurs at the surface of a liquid, molecules at the surface gain enough energy to overcome IMFEvaporation is gradualEven at cold temperatures, some molecules have enough energy to break the attractions and become gas.Evaporation is how your body cools itselfWater in sweat absorbs heat from your bodyWater evaporates leaving less heat in your body and a lower ‘average kinetic energy’ (lower temperature)
26Phase Changes temp v.p. IMF v.p. Vapor Pressure pressure of vapor above a liquid at equilibriumv.p.depends on temp & IMFtemptempv.p.IMFv.p.
27Phase Changes Patm b.p. IMF b.p. Boiling Point Temperature at which the vapor pressure of a liquid equals the external atmospheric pressuredepends on Patm & IMFNormal B.P. - b.p. at 1 atmPatmb.p.IMFb.p.
28SublimationSublimation - when a substance goes from solid directly to gas without becoming a liquidSolid iodineFrozen carbon dioxide (dry ice)Moth balls (p-dichlorobenzene)Solid air freshenersIce cubes left in a freezer for a long time
29Phase Changes the Release Energy CondensationDepositionFreezing
30Condensation Condensation – process of changing from gas to liquid When molecule s lose energy,Velocity of the molecules is reducedIntermolecular forces take overHydrogen bonds form, energy is released (heat comes out)There are different causes for condensation, however, all involve loss of energy:Contact with cold item
31Phase Changes Equilibrium trapped molecules reach a balance between evaporation & condensation
32DepositionDeposition – changing from gas directly to solidSnowflakes
33Freezing Freezing – process of changing from liquid to solid Remove energy from liquidMolecules don’t move past each other any longerMolecules stay in fixed, set positionBecome solid
34Phase Changes Energy Required Energy Released Solid Liquid Melting or fusionLiquid SolidfreezingLiquid GasVaporization, evaporation or boilingGas LiquidcondensationSolid GassublimationGas Solidsolidification
35Phase DiagramsPhase diagram shows phase of matter at different temperatures and pressuresEach substance is uniqueX-axis usually temperatureY-axis usually pressureThere is usually a “Triple Point” where all three phases can coexist“Critical Point” – temperature and pressure above which substance cannot exist as liquid
38Heating CurvesKinetic Energy Changes – Heat Energy speeds up the molecules.Potential Energy Changes – Heat energy separates the molecules from solid to liquid, liquid to gas.
39Heating Curves Temperature Change change in KE (molecular motion) depends on heat capacityHeat Capacityenergy required to raise the temp of 1 gram of a substance by 1°C
40Phase ChangeThe energy involved in a phase change is calculated using:Heat of Fusion (Hfus)Heat of Vaporization (Hvap)
41Heat of FusionHeat 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 orliquid solid
42Heat of Vaporization Heat of Vaporization (Hvap) energy required to boil 1 gram of a substance at its b.p.EX: sweating, steam burns, the drinking bird