05_-_Liquids_Solids_and_Solutions

05_-_Liquids_Solids_and_Solutions -...

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ChE 102: Chemistry for Engineers Chapters 12 & 13 – Liquids, Solids, and Solutions
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05 - Liquids, Solids, and Solutions 2 Enthalpy of Vapourization (12.2) Vapourization (evaporation) – the passage of molecules from the surface of a liquid into the vapour state. Increases with: Increase in temperature Increase in liquid surface area Decrease in intermolecular forces Condensation – conversion of a vapour to a liquid Enthalpy of Vapourization ( Δ H vapourization ) – the quantity of heat that must be absorbed to vapourize a certain quantity of liquid at a constant temperature. Δ H condensation = - Δ H vapourization
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05 - Liquids, Solids, and Solutions 3 Phase Equilibrium Water in an open vessel would evaporate completely At phase equilibrium (water in a closed vessel - (c) ): Equilibrium is a dynamic process No net conversion from one phase to another Properties are uniform throughout
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05 - Liquids, Solids, and Solutions 4 Vapour Pressure Vapour pressure ( P vap ) is the pressure measured when the system reaches phase equilibrium Dependent on temperature and gas type An intensive property (independent of system size) Example: H 2 O at 25 ° C has P vap = 23.8 mmHg For mixtures at equilibrium, the partial pressure of each component is given by P vap
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05 - Liquids, Solids, and Solutions 5 Vapour Pressure of Water
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05 - Liquids, Solids, and Solutions 6 Vapour Pressures of Selected Liquids Boiling Point – where the pressure of the escaping molecules equals that of the molecules in the vapour phase above Normal Boiling Point (at P = 760 mmHg): a) Diethyl ether (C 4 H 10 O) b) Benzene (C 6 H 6 ) c) Water (H 2 O) d) Toluene (C 7 H 8 ) e) Aniline (C 6 H 7 N)
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05 - Liquids, Solids, and Solutions 7 Vapour Pressure Curves
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05 - Liquids, Solids, and Solutions 8 Antoine’s Equation for  P vap Vapour pressure of a compound is a strong function of temperature The most important correlation for vapour pressure is Antoine’s equation : A , B and C are constants that depend on the type of substance in a given temperature range Antoine’s equation is an empirical equation – it is based on the observation that plots of log 10 P vap versus 1 / T are approximately linear T C B A P vap + - = 10 log
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05 - Liquids, Solids, and Solutions 9 Energy Changes During Phase Changes Energy (heat) is necessary to accomplish a phase transition (vapourization, liquefaction or sublimation) H 2 O ( l ) + 44.01 kJ/mol H 2 O ( g ) @ 25 ° C and 1 atm: Δ H vap = 44.01 kJ/mol H 2 O ( g ) – 44.01 kJ/mol H 2 O ( l ) @ 25 ° C and 1 atm: Δ H liq = –44.01 kJ/mol
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05 - Liquids, Solids, and Solutions 10 Clausius-Clapeyron Equation for  P vap Another useful equation correlating P vap to temperature is the Clausius-Clapeyron equation : T is in K Δ H vap is assumed not to vary with changes in temperature Clausius-Clapeyron equation is a
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