Presentation on theme: "Physical change of matter from one phase to another due to a transfer of energy. Phase Changes."— Presentation transcript:
Physical change of matter from one phase to another due to a transfer of energy. Phase Changes
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). Evaporation
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. Condensation
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.
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. Boiling
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. Freezing
Melting Solid – 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.
Solid - gas. Example: mothballs that evaporate without leaving a liquid, and when snow on the ground evaporates skipping the liquid phase altogether. Sublimation
Temperature °C Phase Change Diagram Heat Energy Freezing Melting Condenses Boiling M.P F.P B.P C.P O 100 Heat of fusion Heat of vaporization
Phase Changes From what Phase-to-Phase does change occur Absorb or Release Heat Energy? Cooling or Warming Process Melting Freezing Vaporization Condensation Sublimation solid-liquid Absorb liquid-solid Release liquid-gas Absorb gas-liquid Release solid-gas Absorb Cooling Warming Cooling Warming Cooling
Amount 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? Heat of Fusion 800
Amount 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? Heat of Vaporization 5400
How much heat is required to change 1g of ice at -20°C to water vapor at 130°C? 1.Q = mct 1g · 0.5 cal/g-C · 20 °C = 10 cal. 2.H f 1g · 80 cal/g= 80 cal. 3.Q = mct1g · 1 cal/g-C · 100 °C= 100 cal. 4.H v 1g · 540 cal/g = 540 cal. 5.Q = mct1g. · 0.5 cal/g · 30 °C = 15 cal. Sample Problem 745 calories