C_Unit_3_Phase_Changes_K_2010-2011

C_Unit_3_Phase_Changes_K_2010-2011 - Unit 3: Unit 3: Energy...

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Unformatted text preview: Unit 3: Unit 3: Energy and Energy and Phase Phase Changes_K Changes_K Chapter 13 Cypress Creek Chemistr y Click box to view movie clip. States of Matter Phases • States of substances are called phases when they coexist as physically distinct parts of a mixture, such as ice water. • When energy is added to or taken away from a system, one phase can change into another. Phase Changes • Melting/Freezing • Changes between solid and liquid phases • Vaporization/Condensation • Changes between liquid and gas phases • Sublimation/Deposition • Changes directly between solid and gas phases H eat (Ther mal) Ener gy • Heat is a form of energy that flows between two samples of matter because of their difference in temperature • Heat flows from hot to cold • I t can be absorbed or released • Measured in units of calories or Joules Phase Changes • Endothermic phase changes absorb energy • Sublimation • Vaporization • Melting • Exothermic phase changes release energy • Deposition • Condensation • Freezing Vapor ization • Evaporation • Only occurs at the surface of the liquid at room temperature • Ex: Sweating cools the human body • Boiling • Occurs throughout the liquid • Boiling point occurs when vapor pressure = atmospheric pressure • Ex: Boiling water • Higher altitudes have lower atmospheric pressure, so lower boiling point Phase Diagr ams • Temperature and pressure control the phase of a substance. • A phase diagram is a graph of pressure versus temperature that shows in which phase a substance exists under different conditions of temperature and pressure. • A phase diagram has three regions, each a different phase and three curves that separate each phase. • The points on the curves indicate conditions under which two phases coexist. Phase Diagr ams Sublimation point Freezing point Boiling point Phase Diagr ams • Standard Pressure Line (1 atm, or equivalent) • Normal Freezing Point • Temp at which standard pressure meets the solid-liquid curve • Normal Boiling Point • Temp at which standard pressure meets the liquid-vapor Normal Boiling Point Normal Freezing Point STP Phase Diagr ams...
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This note was uploaded on 09/27/2011 for the course CHEM idk taught by Professor All during the Spring '11 term at University of Houston.

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C_Unit_3_Phase_Changes_K_2010-2011 - Unit 3: Unit 3: Energy...

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