chapter 8 slides

chapter 8 slides - Physical Equilibria Chapter 8 CHEM 6B...

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Physical Equilibria Chapter 8 CHEM 6B Dr. DiPasquale CHEMICAL PRINCIPLES: A Quest for Insight – Atkins & Jones
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Phases and Phase Transitions z A single substance can exist in different phases, or different physical forms: solid, liquid, and gas. z Changing from one phase to another is called a phase transition. z Phase transitions take place at specific temperatures and pressures that depend on the purity of the substance. z Sea water melts at a lower temperature and boils at a higher temperature than distilled water.
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Vapor Pressure z The presence of a vapor pressure for a liquid is a sign that the condensed phase (liquid) and the vapor phase are in dynamic equilibrium. z Vapor pressure – the characteristic pressure that the vapor phase of a liquid/vapor equilibrium exerts on the atmosphere regardless of the amount of liquid present. z 0.01 mL H 2 O will exert the same vapor pressure as an entire swimming pool of water.
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Volatility z Liquids with high vapor pressures at ordinary temperatures are said to be volatile (evaporate quickly/easily). z The stronger the intermolecular forces between molecules, the less volatile the substance. z Ionic compounds are less volatile than coordination compounds, which are less volatile than polar-covalent (H bonding) compounds, which are less volatile than non-polar covalent compounds.
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Volatility
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Vapor Pressure at Equilibrium
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Vapor Pressure at Equilibrium z Δ G vap = G m (g) G m (l) = 0 z For an ideal gas, G m (g) ( P ) = G m ° (g) + RT ln P z Δ G vap = Δ G vap °+ RT ln P = 0 z Δ G vap ° is the standard free energy of vaporization z ln P = – Δ G vap °/ RT z Using Δ G vap °= Δ H vap °–T Δ S vap ° z ln P = – Δ H vap °/ RT + Δ S vap °/ R z P = Ae - Δ H / RT where A = e Δ / R
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Vapor Pressure and Temperature z The vapor pressure of a liquid increases as the temperature increases (as e - Δ H / RT ). z The Clausius-Clapeyron equation gives the quantitative dependence of the vapor pressure of a liquid on temperature: o vap 2 11 2 ln H P P RT T Δ ⎛⎞ =− ⎜⎟ ⎝⎠
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Vapor Pressure and Temperature
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Boiling z When the temperature of a liquid is raised to the point at which the vapor pressure is equal to the
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This note was uploaded on 01/25/2011 for the course CHEM 6BL taught by Professor Berniolles during the Spring '08 term at UCSD.

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chapter 8 slides - Physical Equilibria Chapter 8 CHEM 6B...

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