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UB CHE 102 - The Solution Process, Colligative Properties

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Chem 102 1st Edition Lecture 1Outline of Current Lecture – Chapter 13I. The Solution ProcessA. Energy Changes and Solution FormationII. Expressing Concentration (formulas)III. Solution: Saturation and SolubilityIV. Henry’s LawV. Colligative PropertiesA. Freezing Point DepressionB. Raoult’s Law, VaporC. Boiling Point ElevationCurrent LectureI. The Solution Process-a solution is a homogeneous mixture of a solute (small amount and a solvent (large amount) -An electrolyte is when some solutes dissolve to give ions surrounded by solvent molecules (NaCl). Whereas a non-electrolyte is when some solutes dissolve to give molecules surrounded by solvent molecules (Sugar). -In the solutionprocess intermolecular forces become rearrangedA. There are 3 energy steps in forming solutions 1. The separation of solute molecules 2.The separation of solvent molecules and 3. The formation of a solute-solvent interaction –Enthalpy is the change in the solution process:ΔH(solution) = ΔH(solute) + ΔH(solvent) + ΔH(mix) -When intermolecular forces are broken the process is endothermic (+,positive)-When intermolecular forces are formed the process is exothermic (-, negative)-*****RULE FOR SOLUTION FORMATION: polar solvent will dissolve polar solutes but non-polar solvents will dissolve non-polar solutes- A Spontaneous Process is when the process occurs without 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.outside intervention, the spontaneous process always leads to a greater state of disorder within the solution, and sometimes the spontaneous process decreases the energy of thesystemII. Expressing Concentration- concentration is the amount of solute per solvent in mass, moles, or litersSIMPLE CONCENTRATION EQUATIONS TO KNOWIII. Solution: Saturation and Solubility-Dissolve- Solute+Solvent Solution-Crystallization- SolutionSolute+Solvent-Saturation- Solution in equilibrium with undissolved solute-Solubility- Maximum amount of solute needed to form a saturated solution -Supersaturated- Greater amount of solute than needed toform saturated solution -Miscible- Liquids that mix in any proportions-Inmiscible- Liquids that do not dissolve in one another-The number of –OH groups within a molecule increase the solubility in waterIV. Henry’s Law-Henry’s law states that the concentration of a gaseous solute dissolved in a liquid solvent increases linearly as the partial pressure of the gas is in contact with the solution:*The proportionality constant k, known as the Henry’s Law constant, is a characteristic of the gas and depends on temperature and the solvent. The value of k increases as DHmix becomes more negative (that is, solute-solvent forces become stronger) and decreases with increasing temperature*V. Colligative Properties-depend on the quantity of solute molecules or ions, not their identities. These properties include Freezing Point, Vapor, Boling Point, and Osmotic PressureA. Freezing Point Depression- at freezing point solid solvent is in equilibrium with solvent molecules in solution. This means that the rate at which solvent molecules go from crystals to solution equals the rate at which solvent molecules in solution crystallize. -Lower temperature is required so that the rate of crystallization= rate of melting-The solution freezes at a lower temperature (DTf) than the pure solvent.Sgas = kPgas-van’t Hoff factor iis the number of particles formed in solution when one formula unit of the solute dissolves in the solvent (e.g., i = 1 for a non-electrolyte, i = 2 for NaClin water).-Decrease in freezing point (DTf) is directly proportional to molality times the van’tHoff factor i (Kfis the molal freezing-point-depression constant)B. Raoult’s Law- If PA is the vapor pressure with solute, PA° is the vapor pressure without solvent, and CA is the mole fraction of A in solution, then: -An ideal solution is one that obeys Raoult’s Law -Raoult’s Law breaks down when solvent-solvent and solute-solute intermolecular forcesare greater than solute-solvent intermolecular forcesC. Boiling Point Elevation-A nonvolatile solute lowers the Vapor Pressure of a volatile solvent-Our goal in Chem 102 for BP elevation is to be able to read the phase diagram for a solution:-Molal boiling-point-elevation constant, Kb, expresses how much DTb changes with molality,


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