Presentation on theme: "Phase Changes Physical change of matter from one phase to another due to a transfer of energy."— Presentation transcript:
1 Phase ChangesPhysical change of matter from one phase to another due to a transfer of energy.
2 Evaporation Liquid – gas at surface of a liquid. Molecules gain KE to become a vapor. Molecules left behind lose KE.Cooling process – molecules left behind lose KE (cooler).
3 Condensation Gas – liquid. Gas molecules ↓KE when collide with cold surface. Condense to liquid phase.Warming process – KE lost by condensing gas molecules warms the surface they strike.
4 Evaporation-Condensation Rates Depends upon environment, if moist:Condensation > evaporation (warming)Evaporation > condensation (cooling)Equilibrium – state of balance. Evaporation and condensation occurring at equal rates.
5 Boiling Liquid – gas beneath the surface of a liquid. Bubbles of vapor form beneath the surface – rise – break free to the vapor phase.↑atm. pressure - ↑boiling pt.Cooling process – the water is being cooled relative to the ↑temp it would attain otherwise. Because of cooling, it remains 100 °C instead of getting hotter.
6 Freezing Liquid - solid. Energy is extracted, molecules slow down and the molecular attraction overcomes the KE.Warming process – when you make ice cubes, you put liquid water in the freezer. The freezer cools the water, taking energy out – so it must give off energy.
7 MeltingSolid – liquid.Heat energy is added until KE is greater than the molecular attraction.Cooling process – the source of energy is the object or material around the stuff that is melting. The source cools as energy goes to the melting object.
8 Sublimation Solid - gas. Example: mothballs that “evaporate” without leaving a liquid, and when snow on the ground “evaporates” skipping the liquid phase altogether.
10 Phase Change Diagram Temperature °C Heat Energy Heat of vaporization C.PCondensesHeat of fusionTemperature °C100BoilingF.PB.PFreezingOMeltingM.PHeat Energy
11 Phase Changes Phase Changes Melting Freezing Vaporization Condensation From what Phase-to-Phase does change occurAbsorb or Release Heat Energy?Cooling or Warming ProcessMeltingFreezingVaporizationCondensationSublimationsolid-liquidAbsorbCoolingliquid-solidReleaseWarmingliquid-gasAbsorbCoolinggas-liquidReleaseWarmingsolid-gasAbsorbCooling
12 Heat of FusionAmount of heat needed to change 1g substance from solid – liquid phase.80 calories/g for water.Example: How many calories are needed to change 10g of ice at 0 °C to 10g of water at 0 °C?800
13 Heat of VaporizationAmount of heat needed to change 1g substance from liquid – gas phase.540 calories/g for water.Example: How many calories are needed to change 10g of water at 100 °C to entirely to water vapor?5400
14 Sample ProblemHow much heat is required to change 1g of ice at -20°C to water vapor at 130°C?Q = mc∆t 1g · 0.5 cal/g-C · 20 °C = 10 cal.Hf 1g · 80 cal/g = 80 cal.Q = mc∆t 1g · 1 cal/g-C · 100 °C = 100 cal.Hv 1g · 540 cal/g = 540 cal.Q = mc∆t 1g. · 0.5 cal/g · 30 °C = 15 cal.745 calories