CHEM1212: Chapter 13 Notes
CHEM1212: Chapter 13 Notes CHEM1212
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This 5 page Class Notes was uploaded by Brittany Ariana Borzillo on Friday September 16, 2016. The Class Notes belongs to CHEM1212 at University of Georgia taught by Donald Wayne Suggs in Fall 2015. Since its upload, it has received 6 views. For similar materials see Freshman Chemistry II in Chemistry at University of Georgia.
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Date Created: 09/16/16
CHAPTER 13 Review of Solubility Solubility o Quantitative measure of the amount of solute that will dissolve in a solvent at a given temperature o Solute substances dissolve in solvent, insoluble don’t Saturated o Solution is one in which the solute concentration is at the solubility limit at a given temperature Unsaturated o Solute concentration is less than the solubility limit as a given temperature Miscible o Two liquids mix completely o Homogeneous solution Immiscible o Two liquids don’t intermix o Heterogeneous mixture Concentration Units Molarity (M) o Amount of moles of solute dissolved in 1L of solution Weight Percent (%) o Mass of solute in 100g solution Molality (m) o moles of solute dissolved in 1kg solvent Mole Fraction (XA) o Moles of component A per total moles of solution Parts per Million (ppm) o Mass of solute (g) in 10 grams of solvent Parts per Billion (ppb) o Mass of solute (g) in 10 grams of solvent Entropy and Thermodynamic Control Entropy o A measure of the dissipated energy within a system that is unable to do work at a given temperature o A measure of disorder within a system o Closely linked to the mobility of atoms and molecules Higher entropy represents more free movement o Closely linked to temperature Directly proportional with entropy and mobility Enthalpy change for a dissolution process is related to the difference between the strength of intermolecular forces in the pure substances and the intermolecular forces between the species in the solution o If the forces in the solution are stronger, the enthalpy is endothermic o If the forces in the solution are stronger the enthalpy is exothermic Generally reactions that increase the free motion of molecules and/or form stronger intermolecular forces are favored When a reaction is favored either the enthalpy or entropy and not favored by the opposite its dependent on temperature o Entropy favored/enthalpy disfavored Favored at higher temperatures o Entropy disfavored/enthalpy favored Favored at lower temperatures Gas-Gas Mixtures Mixing gasses is entropy favored Enthalpy has no role in gas mixing because gases don’t have intermolecular forces o Mixing gasses is favored at any temperature Liquid-Liquid Mixtures Depend on enthalpy and entropy whether substances are miscible “like dissolves like” o polar molecules can only be dissolved in polar molecules o nonpolar molecules can only be dissolved in nonpolar molecules Solid-Liquid Mixtures “like dissolves like” applicable o ionic compounds will dissolve in polar solutions o ion-dipole forces electrostatic force between an ion and a neutral molecule with a permanent dipole movement H hydration o enthalpy of hydration o enthalpy change when one mole of a gaseous ion dissolces in water o Coulomb’s Law Ion size increases, the species attracted to one another are further apart Hhydrationcreases ion charge increases, the attractive force increases Hhydrationcreases o small radius + large charge = more negative H hydration entropy manipulates the dissociation of ionic compounds in water o water surrounds ions to form a hydrated complex smaller ions have larger hydration numbers larger charges have larger hydration numbers the impact of entropy on dissolutions is more significant for ionic compounds containing small highly charged ions Pressure Effects: Solubility Gas in Liquid pressure has a large effect on solubility of gases in liquid but negligible effect on solubility of liquid or solid in liquid in a closed system a liquid and gas will form an equilibrium where the rate at which gas molecules are dissolving in and escaping from the solution are equal and the amount of dissolved gas is constant o solvent molecules surround has while dissolved gas molecules find their way to the surface as pressure increases, there are more collisions between gas and solvent which increases the rate of dissolution o new equilibrium must be established with the greater amount of dissolved gas Henry’s Law o The solubility of a gas is proportional to the pressure of the gas above the solution Temperature Effect on Solubility Temperature effects the entropy and enthalpy of a system o As temperature increases, entropy increases o Enthalpy change depends on the solute, solvent, intermolecular forces, and enthalpy change of dissolution Temperatures effect on solubility is dependent on strength of intermolecular forces, hydration of ions, when dissolved and more Enthalpy of dissolution (heat of solution) o The amount of heat involved in the process of forming a solution o As a solid dissolves it absorbs the heat energy from the solvent Colligative Properties Properties that are related to the concentration of solute particles The properties and type of solute are irrelevant Osmotic Pressure o Osmosis The flow of solvent through a semipermeable membrane (a thin sheet of material through which only certain species of chemicals can pass) from a solution of lower concentration to a solution of higher concentration in effort of establishing equilibrium o Osmotic Pressure The amount of pressure required to prevent the flow of a solvent across a semipermeable membrane Proportional to the concentration of solute particles in solution In nonelectrolytes the concentration of particles is equal to the concentration of the solute In electrolytes the number of particles produces per solute particle is taken into account o Van’t Hoff Factor Ratio of the experimentally measured freezing point depression of a solution to the value of apparent molality Basically a ration of ions produced after dissolving a solute in solution o Solutions Isotonic Solute concentration inside and outside cell are identical Hypotonic Solute concentration is lower outside the cell with respect to the cell Hypertonic Solute concentration is higher outside the cell with respect to the cell Vapor Pressure Lowering o Vapor pressure, when in dynamic equilibrium with the liquid, is a function of temperature and intermolecular forces Adding a solute to a liquid will lower equilibrium vapor pressure o Volatility Tendency for molecules of a substance to escape into the gas phase o When the solute is added to solvent, the solute particles block solvent molecules from escaping into the vapor phase but do not block vapor molecules from reentering the liquid phase Boiling Point Elevation The boiling point of a solvent in a solution is always higher than that of the pure solvent Freezing Point Depression Freezing point depression of a solvent in solution is always lower than the freezing point of the pure solvent Alloys Mixtures of different metals often in the solid state o Can be heterogeneous Crystalline regions of metals intermixed o Can be homogeneous Two or more metals completely mixed o Amalgams Mercury is the solvent Colloids Mixture where one substance is distributed uniformly throughout another o Particles are larger than the size of a molecule but invisible to the eye Classified according to phases of components o Sol Colloidal dispersion of solid substance in a fluid medium o Gel Colloidal dispersion with a structure that prevents it from flowing Emulsion o Heterogeneous mixture of two liquids that does not separate into two distinct phases o Emulsifiers Allow two immiscible substances to form a mixture Surfactant Both polar and nonpolar Aerosols o Mixture of small particles in gas o
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