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Lecture13222
 

Lecture13222

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a supplemental resource for students

a supplemental resource for students

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    Lecture13222 Lecture13222 Presentation Transcript

    • Liquid and Solid States: Qualitative Aspects of Phase Changes Lecture 13
    • Three states of matter everywhere.
    • We consume water in three states
    • There are states of matter and phases. Do not confuse them.
    • Two types of electrostatic forces at work:
      • Intramolecular (bonding) forces exist within each molecule and influence the chemical properties of the substance;
      • Intermolecular (nonbonding) forces exist between the molecules and influence the physical properties of the substance.
    • A macroscopic comparison:
      • Gas conforms to shape and volume of container, has high compressibility and ability to flow.
      • Liquid conforms to shape of container, its volume is limited by surface. It has very low compressibility and moderate ability to flow.
      • Solid maintains its own shape and volume, has almost no compressibility and ability to flow.
    • Phase changes
    • Phase change definitions
      • Melting (fusion) is a process when a solid liquifies.
      • Freezing (crystallization) is a process when a liquid solidifies.
      • Vaporization is a process when a liquid vaporizes.
      • Condensation is a process when a gas changes into a liquid.
    • Phase changes
    • Phase change definitions
      • Sublimation is a process when a a solid becomes a gas without first becoming a liquid.
      • Deposition is a process when a a gas becomes a solid without first becoming a liquid.
    • How enthalpy changes
      • Melting and vaporizing are endothermic processes.
      • Condensing and freezing are exothermic processes.
    • Each phase change has a specific  H.
      • H 2 O (l)  H 2 O (g) ;  H vaporization
      • H 2 O (g)  H 2 O (l) ;  H condensation
      • H 2 O (s)  H 2 O (l) ;  H fusion
      • H 2 O (l)  H 2 O (s) ;  H crystallization
      • I 2(s)  I 2 (g) ;  H sublimation
      • I 2(g)  I 2 (s) ;  H deposition
    • All the reverse processes have  H of the same magnitude but opposite sign:
      •  H vaporization = —  H condensation
      •  H fusion = —  H crystallization
      •  H sublimation = —  H deposition
    • Enthalpy of phase changes
    • Enthalpy of phase changes
    • Heat of sublimation equals sum of the heats of fusion and vaporization:
      • Solid  liquid;  H o fus
      • Liquid  gas;  H o vap
      • -----------------------------
      • Solid  gas;  H o subl
    • Heating water
    •  
    • Phase changes of many substances are reversible and reach equilibrium.
    • Liquid-gas equilibrium
    • When a system at equilibrium is disturbed, it counteracts the disturbance and eventually re-establishes a state of equilibrium.
    • Molecular speed vs temperature
    • The higher the temperature is, the higher the vapor pressure. The weaker the intermolecular forces are, the higher the vapor pressure.
    • Vapor pressure vs temperature
    • Vapor pressure vs temperature
      • Rudolf Julius Emanuel Clausius (1822–1888), German scientist
      • Benoît Paul Émile Clapeyron (1799-1864), French scientist
    • The Clausius-Clapeyron equation:
    • A sample problem on using the Clausius-Clapeyron equation.
    • The boiling point is the temperature at which the vapor pressure equals the external pressure. The boiling point depends on the applied pressure.
    • Solid, liquid, gas
    • Phase diagram of CO 2
    • Features of phase diagram:
      • Regions correspond to different phases of the substance.
      • Lines between regions represent the phase transition curves.
    • Features of phase diagram:
      • The critical point shows critical temperature and pressure, at which the phase boundary disappears.
      • The triple point shows temperature and pressure, at which all phases co-exist.
    • Phase diagram of H 2 O
    • THE END