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Phase Changes and Heating Curves: Flashcards

Revise the six phase changes, heating curves, enthalpies of fusion and vaporization, and vapour pressure.

10 cardsIntermediate

10 cards

  1. Question
    Name the six phase changes.
    Answer

    Melting, freezing, vaporization, condensation, sublimation, deposition.

  2. Question
    Which phase changes are endothermic?
    Answer

    Melting, vaporization and sublimation (particles are pulled apart).

  3. Question
    Why does the temperature stay constant while ice melts?
    Answer

    All the heat goes into overcoming intermolecular forces, not into increasing the kinetic energy of the particles.

  4. Question
    Which equation is used on the flat parts of a heating curve?
    Answer

    q=nΔHq = n\Delta H (ΔH of fusion or vaporization).

  5. Question
    Which equation is used on the sloped parts of a heating curve?
    Answer

    q=mcΔTq = mc\Delta T, with the specific heat capacity of that state.

  6. Question
    Give ΔH(fus) and ΔH(vap) for water.
    Answer

    6.01 kJ/mol and 40.7 kJ/mol.

  7. Question
    Why is ΔH(vap) much larger than ΔH(fus)?
    Answer

    Vaporizing separates the molecules completely; melting only loosens them.

  8. Question
    When does a liquid boil?
    Answer

    When its vapour pressure equals the external pressure.

  9. Question
    Why does water boil below 100 °C on a mountain?
    Answer

    The air pressure is lower, so the vapour pressure reaches it at a lower temperature.

  10. Question
    How much heat melts 100. g of ice at 0 °C?
    Answer

    (100. g ÷ 18.02 g/mol) × 6.01 kJ/mol = 33.4 kJ