CHEM 135 1st Edition Lecture 4 Outline of Last Lecture I Solids a Cubic unit cell b Classification of crystalline solids Outline of Current Lecture II Solutions a Definitions and components b Types of formations III Solubility a Effect of temperature b Effect of pressure IV Colligative Properties V Vapor Pressure and Dynamic Equilibrium VI Raoult s Law Current Lecture II a Definitions Solution a homogeneous mixture of two or more substances Solvent the majority component of a solution Solute the minority component of a solution b Types of Formations Enthalpy of the solution Hsolution Hsolute Hsolvent Hmix H1 Separation of solute molecules the enthalpy needed for separation is positive making this separation endothermic due to the energy required to break the bonds within the solute molecules These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute H2 Separation of solvent molecules Again separation enthalpy endothermic reaction H3 Formation of solute solvent interactions The formation of new bonds enthalpy due to the energy being released exothermic reaction Exothermic solution formation Hsolute Hsolvent Hmix releasing heat Endothermic solution formation Hsolute Hsolvent Hmix absorbing heat Saturated solution contains max amount of solute cannot dissolve any more solute if added Unsaturated solution contains less solute than the max capacity can dissolve more solute Supersaturated solution contains more solute then the max capacity contains excess undissolved solute III Solubility Solubility the amount of solute that can dissolve in a given amount of solvent at a given temperature When most solids are placed in water solubility increases as temperature increases o Why Bonds break easier when heated allowing for the solute to dissolve faster Solubility of a gas in a liquid increases with increasing pressure of the gas above the liquid o Henry s Law Sgas kHPgas IV Colligative Properties These are properties that depend ONLY on the number not the type of solute particles in a solution o Vapor Pressure Lowering o Freezing Point Depression o Boiling Point Elevation o Osmotic Pressure V Vapor Pressure and Dynamic Equilibrium Dynamic equilibrium rate of evap rate of condensation Vapor Pressure Pressure of a gas in dynamic equilibrium with its liquid Ex If a non volatile liquid doesn t evaporate easily solute is added to a liquid what happens o Vapor pressure of solution is lowered VI Raoult s Law Vapor Pressure of the solution is given by Psolution Xsolvent P solvent Xsolvent mole fraction of the solvent n solvent n solute n solvent Vapor pressure lowering P P Xsolvent P solvent