Given a temperature and pressure phase diagrams tell us which phase will exist Features of a phase diagram Triple point temperature and pressure at which all three phases are in equilibrium Vaporpressure curve generally as pressure increases temperature increases ID: 682996
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Slide1
Phase Diagrams
Phase diagram: plot of pressure vs. Temperature summarizing all equilibria between phases.Given a temperature and pressure, phase diagrams tell us which phase will exist.Features of a phase diagram:Triple point: temperature and pressure at which all three phases are in equilibrium. Vapor-pressure curve: generally as pressure increases, temperature increases.Critical point: critical temperature and pressure for the gas.Melting point curve: as pressure increases, the solid phase is favored if the solid is more dense than the liquid.Normal melting point: melting point at 1 atm.
videoSlide2
Phase Diagrams
Any temperature and pressure combination not on a curve represents a single phase.Slide3
Phase Diagrams
The Phase Diagrams of H2O and CO2Water:The melting point curve slopes to the left because ice is less dense than water.Triple point occurs at 0.0098C and 4.58 mmHg.
Normal melting (freezing) point is 0
C.
Normal boiling point is 100
C.
Critical point is 374
C and 218 atm.
Carbon Dioxide:
Triple point occurs at -56.4
C and 5.11 atm.
Normal sublimation point is -78.5
C. (At 1 atm CO
2
sublimes it does not melt.)
Critical point occurs at 31.1
C and 73 atm.Slide4
Phase Diagrams
The Phase Diagrams of H2O and CO2Slide5
Critical Point: indicates the critical temperature and critical pressureCritical Temperature: temperature above which the substance cannot exist in the liquid stateCritical Pressure: lowest pressure at which the substance can exist as a liquid at the critical temperatureSlide6
Substance
T (K)P (kPa*)Acetylene192.4120Ammonia195.40
6.076
Argon
83.81
68.9
Butane
[5]
134.6
7 × 10
−4
Carbon (
graphite
)
476510132Carbon dioxide216.55517Carbon monoxide68.1015.37Chloroform[6]175.430.870Deuterium18.6317.1Ethane89.898 × 10−4Ethanol[7]1504.3 × 10−7Ethylene104.00.12Formic acid[8]281.402.2
Triple Point of WaterSlide7
At the critical point C, the properties of the gas and liquid phases approach one another, resulting in only one phase: a homogeneous supercritical fluid
It can diffuse through solids like a gas, and dissolve materials like a liquidSlide8
Copyright 1999, PRENTICE HALLChapter 11
8Supercritical CO2 Used to Decaffeinate Coffeeis any substance at a temperature and pressure above its critical pointSlide9
ApplicationsDecaffeinating coffeeSolvents for dry-cleaningRefrigerationBiodiesel productionSlide10
Ice melts at a higher temperature with decreasing pressureSlide11
ApplicationFreeze drying food: freeze food and then lower pressure so ice sublimes