Gen Chem 11 week 4 notes
Gen Chem 11 week 4 notes 603613
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This 4 page Class Notes was uploaded by Emmanuel Notetaker on Sunday February 7, 2016. The Class Notes belongs to 603613 at University of Cincinnati taught by waddell, D in Winter 2016. Since its upload, it has received 48 views. For similar materials see Gen Chem II in Chemistry at University of Cincinnati.
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Date Created: 02/07/16
Chap 13: The Properties of Mixture; Solution and Colloids Mixture 2+ substances mixed together physically composition is variable retains some properties of its components Colloid (Heterogeneous Mixture) has 1+ visible boundaries between its components composition is NOT uniform; varies from region to region Solution (Homogeneous Mixture) no visible boundaries b/c particles are individual atoms, ions, small molecules composition IS uniform Solvent Properties of Water polarity and H bonding ability(also has bent molecular shape) ←most important: dissolves ionic compounds using dipoledipole forces and separating ions from solid and keeping them in solution dissolves polar nonionic substance (glucose or ethanol) using H bonding dissolves nonpolar gases (to an extent) through dipoleinduced dipole and dispersion forces Electrolyte A substance that conducts a current when dissolved in water separates ions as it dissolves Strong Electrolyte Soluble ionic compounds they dissociate completely and conduct a large current 1 mole of compound dissolves to yield amount (mole) of ions shown in formula unit (soluble salts, strong acids and bases) Nonelectrolytes do not separate into ions, remain intact molecules soluble covalent substances do not conduct an electric current 1 mole of compound dissolves to yield 1 mole of particles (sugars, alcohols) Vapor Pressure Pressure exerted by the vapor at equilibrium of the liquid of that temperature (equilibrium between liquid and gas) higher temperature, higher VP weaker forces, higher VP Boiling Point Temperature at which the vapor pressure equals the external pressure Polarizability how easily an electron cloud can be distorted smaller atoms/ions are less polarizable than larger ones because their electrons are closer to the nucleus and held more tightly polarizability increases down a group and decreases across a period IonInduced Dipole Forces rely on polarizability arise when ion's charge distorts electron cloud of nearby Nonpolar molecule DipoleInduced Dipole Forces rely on polarizability arise when polar molecule distorts electron cloud of nonpolar molecule weaker then ioninduced b/c charge of each pole <ion's (Coulomb's Law)permanent dipole moment Dispersion (London) Force Between nonpolar molecules increases with more electrons (longer molecules/larger atoms) present between all particles b/c caused by motion of electrons in atoms can fluctuate at any moment, time avg. dipole moment=0 Solvent Generally more abundant component (dissolves solute) usually its physical state determines that of solution Solute less abundant component dissolves in a solvent to form a solution Miscible Substances are soluble in each other in any proportion(solute/solvent lose meaning) Solubility (S) max amt that dissolves in a quantity of given solvent at a given temp where excess solute is present Vary between Solutes Thermochemical Solution Cycle Step 1. Solute particles separate ∆Hsolute>0 Step 2. Solvent particles separate ∆Hsolvent>0 Step 3. Solute & Solvent particles mix & form solution ∆Hmix < 0 ∆Hsoln =∆Hsolute + ∆Hsolvent + ∆Hmix OR =∆Hsolute + ∆Hhydr if solution is HIGHLY positive, solute may not dissolve well Enthalpy Change of Solvation : process of surrounding a solute particle with solvent particles ∆Hsolvation = ∆Hsolvent + ∆Hmix Hydration solvation in water always exothermic (forms stronger iondipole forces)exhibit trends based on charge density ∆Hhydr = ∆Hsolvent + ∆Hmix Vapor Pressure Lowering(∆P) vapor pressure of solution is ALWAYS lower than VP of the pure solvent Ssoln>Ssolv so fewer particles need to vaporize to reach same entropy fewer particles in gas phase >vapor above soln has lower pressure Lattice Energy(∆Hlattice) highly positive separating of an iconic solute (∆Hsolute) into gaseous ions requires A LOT of energy SO ∆Hsoln=∆Hlattice+∆Hhydr Two(2) Factors that Determine Solubility. 1)∆Hsoln 2)entropy(S) solution formation involves interplay of lower enthalpy and higher entropy Entropy(S) thermodynamic variable directly related to # of ways a system can distribute its energy freedom of motion of particles: natural tendency of system particles to spread out and kinetic energy to disperse Solute Equilibrium When solute dissolving at the same rate as dissolved particles are recrystallizing, concentration remains constant solute(undissolved)⇌solute(dissolved) Saturated Solution: is at equilibrium and contains max amount of dissolved solute at given temp when in the presence of undissolved solution Unsaturated Solution Contains less than the equilibrium concentration of dissolved solute Supersaturated Solution Contains more than the equilibrium concentration and is unstable relative to saturated solution add a seed crystal or tap container and excess solute crystallizes immediately Henry's Law solubility of gas α partial pressure of gas above solution Sgas = Kh * Pgas Kh is Henry's Law constant specific for given gas/solvent combos Raoult's Law Psolvent=Xsolvent * P°solvent Boiling Point Elevation(∆Tb) solution boils at higher temp than pure solvent Tb=temp at which its vapor pressure =ext pressure∆Tb α m or ∆Tb=Kb*m ∆Tb= Tb(soln)Tb(solvent) Freezing Point Depression(∆Tf) solution freezes at lower temp than the pure solvent ∆Tf α m or ∆Tf=Kf*m ∆Tf= Tf(solvent)Tf(solution)
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