Chapter 9 liquids and solids
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Chapter 9 Liquids and Solids. Intro Vocabulary. Gas: no definite shape or volume Remember kinetic theory of gases Liquid: definite volume – no definite shape Some attraction between molecules or atoms Solid: definite shape and volume Strong intermolecular bonding

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Chapter 9 liquids and solids

Chapter 9Liquids and Solids


Intro vocabulary
Intro Vocabulary

  • Gas: no definite shape or volume

    • Remember kinetic theory of gases

  • Liquid: definite volume – no definite shape

    • Some attraction between molecules or atoms

  • Solid: definite shape and volume

    • Strong intermolecular bonding

      1. Molecules are much closer together in liquids and solids than in gases

  • In gases, molecules are separated by ten or more molecular diameters

  • In liquids and solids, the molecules are in contact with each other

    2. Intermolecular forces play a major role in the behavior of liquids and solids, whereas they are negligible in gases


  • B phase transitions
    B. Phase Transitions

    • Q = m c ∆T (use for temperature changes)

    • Q = n ∆H (use for phase changes)

      • Temperature DOES NOT change during a phase change


    Phase transitions
    Phase transitions

    • Melting/Freezing

      • Heat of fusion – energy required to melt/freeze 1 mole of a substance

    • Vaporization/Condensation

      • Heat of vaporization – energy required to vaporize/condense 1 mole of a substance

    • Sublimation/Deposition



    Phase diagrams
    Phase Diagrams

    • A. Heating/Cooling Curves definitions

    • 1. Conversion of a solid to a liquid is:_______________

    • 2. Conversion of a liquid to a solid is:_______________

    • 3. The freezing point = melting point

    • 4. Energy needed to melt a given quantity of solid is

    • called the ___________________________________.


    Examples
    Examples:

    • Example: How much energy is required to melt 100.0 grams of ice? The heat of fusion is 6.01 kJ/mole.


    Examples1
    Examples:

    • Example: How much energy in kJ is required to heat 100.0 grams of liquid water from zero to 100°C, and then vaporize all of it? ∆Hvap= 40.79 kJ/mole


    9 1 liquid vapor equilibrium
    9.1 Liquid - Vapor Equilibrium

    A. Vaporization (evaporation) process in an open container

    - evaporation will continue until all the liquid is gone

    - the energy required for vaporization comes from the surroundings and system

    - vaporization leaves the remaining liquid cooler

    - evaporation will occur below the boiling point of a substance

    - evaporation below the boiling point is slower than at the boiling point


    B enthalpy of vaporization
    B. Enthalpy of vaporization

    • Definition – the amount of energy change that occurs during the vaporization of 1 mole of a substance

      q = n ∆Hvap


    C. Vapor Pressure – the pressure of the gas above a liquid in a closed container; dependent on temperature

    1. Closed container vs. open container

    • In an open container the system includes the surroundings and the liquid will evaporate

    • In a closed system the liquid will evaporate and begin to condense when equilibrium is established between the liquid and gas


    2 dynamic equilibrium
    2. Dynamic Equilibrium in a closed container; dependent on temperature

    • When the rate at which the liquid vaporizes is equal to the rate at which the vapor condenses

    • The liquid level in the container does not change

    • Molecules are constantly moving between phases with no net change


    3 pressure and volume
    3. Pressure and Volume in a closed container; dependent on temperature

    • As long as some liquid remains when equilibrium is established, the equilibrium vapor pressure will be the same regardless of the volume of the container


    E vapor pressure curves and temperature
    E. Vapor Pressure Curves and Temperature in a closed container; dependent on temperature

    1. Relationships

    • Vapor pressure of liquid increases as temperature increases


    2 general graph
    2. General in a closed container; dependent on temperature Graph

    • What does this graph tell you about the relative attraction between molecules for substances a-e?


    Boiling point
    Boiling Point in a closed container; dependent on temperature

    1. Definition:

    • The boiling point is the temperature at which the vapor pressure equals atmospheric pressure

      2. Normal Boiling Point:

      • The boiling point at exactly 1 atm of pressure

        3. Dependency on pressure

    • At a certain temperature, large bubbles form throughout the liquid; i.e., the liquid boils

    • The temperature at which a liquid boils depends on the pressure above it


    Dependency on pressure continued
    Dependency on pressure (continued) in a closed container; dependent on temperature

    • At high elevation, atmospheric pressure is lower, so the boiling point is lower

    • To elevate the boiling point and allow food to cook more quickly, a pressure cooker can be used


    9 3 intermolecular forces
    9.3 Intermolecular Forces in a closed container; dependent on temperature

    • Molecules are the structural units of covalently bonded compounds

    • Properties of molecules:

      • nonconductors of electricity when pure

      • insoluble in water but soluble in nonpolar solvents

      • low melting points

    • These properties depend on the intermolecular forces between the molecules


    A 3 types of intermolecular forces
    A. 3 types of intermolecular forces in a closed container; dependent on temperature

    • Dispersion

    • Dipole-dipole

    • Hydrogen bonding


    Dispersion forces
    Dispersion Forces in a closed container; dependent on temperature

    • Definition – a force of attraction between molecules that is caused by temporary dipoles

      dipole – a molecule with a positive a negative end


    Dispersion forces1
    Dispersion Forces in a closed container; dependent on temperature

    2. All molecules have some dispersion forces acting between them

    temporary dipoles form as a result of the natural movement of e-s in the e- cloud creating areas of positive and negative charge


    Dispersion forces2
    Dispersion Forces in a closed container; dependent on temperature

    3. Strength of dispersion forces

    - all molecules have dispersion forces

    - strength increases with increasing # of e-s


    Dispersion forces3
    Dispersion Forces in a closed container; dependent on temperature

    4. Dispersion forces increase as molar mass increases

    - directly proportional

    - Why? As molar mass increases the # of e-s increases

    - higher Dispersion forces = higher boiling and melting points because molecules tend to “stick together”


    Example 9 3
    Example 9.3 in a closed container; dependent on temperature

    Account for the fact that chlorine is a gas, bromine is a volatile liquid, and iodine is a volatile solid at room temperature.


    C dipole dipole forces
    C. Dipole-Dipole Forces in a closed container; dependent on temperature

    • Definition and example

      - a force of attraction between molecules that is caused by permanent dipoles

      - CO = polar bond resulting in permanent dipole


    2. Higher bp and mp than expected in a closed container; dependent on temperature

    because of the D-D forces the molecules “stick together” and require much more energy for the phase change


    Figure 9 9
    Figure 9.9 in a closed container; dependent on temperature


    Example 9 4
    Example 9.4 in a closed container; dependent on temperature


    D hydrogen bonds
    D. Hydrogen Bonds in a closed container; dependent on temperature

    1.Unusually strong type of dipole force

    • H attached to an N or O or F

    • The H from one molecule is strongly attracted to the negative end of the dipole of another

      • The strong dipole forms from the large difference in electronegativities of H and (N, O, or F)

        2.Hydrogen bonds are the strongest intermolecular force

      • unusually high boiling points (H2O vs. CH4)

      • Small size of H allows the unshared pair from the negative end of the dipole to approach the H closely



    5 unusual properties of water
    5. Unusual properties of Water in a closed container; dependent on temperature

    • Because of H-bonding:

      • High specific heat

      • High boiling point

      • Liquid phase more dense than solid phase = ice floats


    Figure 9 10
    Figure 9.10 in a closed container; dependent on temperature


    Example 9 6
    Example 9.6 in a closed container; dependent on temperature



    Covalent vs intermolecular forces
    Covalent following substances? Rank these substances in order of increasing bp. vs. Intermolecular Forces

    • Three types of intermolecular force

      • Dispersion

      • Dipole

      • Hydrogen bond

    • All three intermolecular forces are weak relative to the strength of a covalent bond

      • Attractive energy in ice is 50 kJ/mol

      • Covalent bond in water is 928 kJ/mol


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