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Understanding Phase Changes: Melting and Boiling Points of Water and CO2

This overview explains the concepts of melting and boiling points, emphasizing the conditions under which solids and liquids transition between states. It details the normal melting and boiling points at 1 atm, the significance of vapor pressure in determining phase transitions, and the critical points of substances. It also explores phase diagrams, illustrating how temperature and pressure affect the state of matter, particularly for water and carbon dioxide (CO2). The unique properties of water's and CO2's phase diagrams, including their slopes and critical points, are highlighted.

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Understanding Phase Changes: Melting and Boiling Points of Water and CO2

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Presentation Transcript

  1. Changes of State

  2. Melting point • As the temp of the solid is increased, a point is eventually reached where the liquid and solid have identical vapor pressures

  3. Vapor pressure of solid and liquid water as a function of temperature

  4. Normal melting pt • The temp at which the solid and liquid states have the same vp under the conditions where the total pressure is 1 atm

  5. Normal boiling pt • Temperature at which the vp of the liquid is exactly 1 atm • boiling occurs when the vp of the liq is equal to the pressure of its environment

  6. PHASE DIAGRAMS

  7. Phase Diagrams • Represent the phases of a substance as a function of temperature and pressure

  8. Phase Diagrams • Shows which state can exist at given temp and pressure • conditions of CLOSED system

  9. Critical temp • temp above which vapor cannot be liquified no matter what pressure is applied

  10. Critical Pressure • Pressure required to produce liquification at the critical temp

  11. Critical point • Defined by critical pressure and temp (374oC, 218 atm) • beyond this point is intermediate “fluid” region

  12. Phase diagram for water • Solid/liquid line has negative slope • mp of water decreases as external pressure increases

  13. Phase diagram for water • Opposite of most substance b/c density of ice less than water at mp

  14. Phase diagram for CO2 • Solid/liquid line has positive slope • solid CO2 is more dense than liquid CO2

  15. Phase diagram for CO2 • Triple point at 5.1 atm and -56.6oC • Critical point at 72.8 atm and 31oC • at 1 atm CO2 sublimes

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