Week 5- IMF's and Vaporization
Week 5- IMF's and Vaporization 112
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This 4 page Class Notes was uploaded by BettyAnn Mead on Saturday February 28, 2015. The Class Notes belongs to 112 at University of Massachusetts taught by Voigtman in Spring2015. Since its upload, it has received 103 views.
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Date Created: 02/28/15
Intermolecular Forces and Liquids Any gas suf ciently cooled condenses to a liquid Why 0 Two gases either mix or react when brought together 0 Two liquids brought into contact either mix react or do not mix lons interact via Coulomb s Law lonic compounds are simply due to the columbic interactions of ions But ions can interact with molecule that are polar and ALSO with molecules that are nonpolar o Iondipole interaction Bonds with polar ion 0 Ioninduced dipole interaction Bonds with nonpolar ion An ion can also induce a dipole in a neutral atom or in a nonpolar molecule Electron density redistributes when an ion is close Dipoledipole is the strongest interaction Hydrogen bonding No DipoleDipole Nonpolar ions Low enthalpy Low vaporization DipoleDipole Interaction Polar ions High enthalpy High vaporization Hydrogen bonding An electronegative atom with one or more lone pair 0 N o F o O 0 Cl once in a while 0 Hydrogen bonding as more interaction which increases the boiling point 0 One water molecule may have up to four hydrogen bonds at any time water is very complicated Hydrogen bonding is a special case of dipoledipole interactions 0 Density usually increases as temperature but in water hydrogen bonding changes that 0 Why all the water doesn t freeze and sh die 0 A molecule can induce a dipole in a nonpolar molecule Dipole can even induce dipole in a neutral atom Two nonpolar molecules or atoms can induce dipoles polarize each other This is called London dispersion or induced dipoleinduced dipole interaction 0 These are the ONLY intermolecular forces between nonpolar molecules 0 Boiling points increase with increasing dvapH Properties of Liquids o Vaporization How does it happen Vapor pressure 0 Boiling points and critical temperatures 0 Surface tension capillary action and viscosity At any given temperature it is the fastest molecules that MAY escape the liquid surface Vaporization Liquid l Vapor o Endothermic dvaoH gt 0 Condensann o Vapor Liquid 0 Exothermic dconH dvapH Normal boiling point is when vapor pressure equals 760 mmHg Also known as 1 atm Critical Temperature and Pressure 0 The critical point is the uppermost point on the vapor pressure curve 0 It s coordinates are the critical temperature and critical pressure Surface tension is due to molecules on the surface being pulled attracted back to the bulk liquid Adhesion Attractive forces between different substances Cohesion Attractive forces between molecules of a given substance Solutions and Their Behavior Solution A homogeneous mixture of two or more substances in a single phase 0 Solution component present in largest amount is called the solvent 0 The other solution components are the solutes Binary Solution One solute dissolved in one solvent Example Salt dissolved in water Dissolving solute in a solvent makes a solution and changes properties of the solvent Why The intermolecular forces are changes there are entropy effects and the properties of solutions depend on the number of solute particles per solvent molecule Solution Concentrations o Molarity Moles of Solute Liter of Solution 0 Symbols M or 0 Example 0100 M NaCl or CI 00023 M o Molarity Drawbacks Molarity depends on solution temperature This means there can be no xed ratio between number of solute particles and number of solvent molecules Colligative Properties Solution properties that depend only on the number of solute particles per solvent molecules and NOT of the solute SO alternative solution concentrations must be speci ed There include mole fraction molality and weight percent mass percent also Mole fraction Xa moles of component a Total Moles Mole fraction of a na na nb Molality Moles Solute kg of Solvent 0 Symbol m 0 Weight Percent 100 mass of a component total mass of mixture 0 Also called mass percent A saturated solution of a solute contains the maximum amount that can stably be dissolved Unsaturated Solution Capable of dissolving even more solute Supersaturated Solution An unstable solution containing more solute than can exist at equilibrium Solubility A substances concentration in equilibrium with un dissolved solute in a saturated solution 0 Rate of Dissolution Rate of precipitation at equilibrium Types of Liquids 0 Polar o Nonpolar quotLike dissolves Likequot 0 Two polar liquids are usually miscible Two nonpolar liquids are usually miscible A polar liquid and a nonpolar liquid are usually immiscible Like liquids tend to be miscible because dmixH 0 exothermic and entropy increases dS gt 0 Unlike liquids are usually immiscible due to entropy factors dS lt 0 quotLike dissolves likequot also applies to molecular solids dissolving in liquids
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