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chem lecture ch12

QuestionAnswer
London dispersion forces weak intermolecular forces arising from induced instantaneous polarization multipoles in molecules. They can act between molecules without permanent multipole moments.they are exhibited by nonpolar molecules.
molar enthalpy of solution, Δ Hsolv The total energy adsorbed or released when a solute dissolves in a solvent at constant pressure
State function a property whose value does not depend on the path taken to reach a specific function or value
To get to the value of ΔHsolv, a two step process is used: Vaporize the solid to obtain individual particles, this requires the lattice energy. Bring the gaseous particles into the solvent, the solvation energy is liberated
generalization: Heats of solution of gases in organic solvents Heats of solution of gases in organic solvents are often endothermic, because the energy required to open up pockets is greater than the energy released by attractions formed between the gas and the solvent molecules.
generalization: Heats of solution for gases in water Heats of solution for gases in water are often exothermic, because water already contains pockets to hold the gas molecules and energy is released, when water and gas molecules interact.
Henry’s Law concentration of gas in liquid at any given temp is proportional to partial pressure of gas above solution. Cgas= kH Pgas. kH= constant, which depends on solvent, solute and temp. law holds true only for low concentrations, low pressures, systems
Percentage by mass = = (mass of solute)/(mass of solution) * 100
Molality = moles of solute/ mass of solvent [moles X Kg^-1)
mole fraction = XA= nA/ nA+nB+nC...+nZ
two assumptions of colligative properties 1.The solute is not volatile, it does not contribute to the vapor pressure. 2. The solute does not dissolve in the solid solvent.
general colligative properties Solutes have an effect on the boiling and freezing points of mixtures and they give rise to an osmotic pressure. In dilute solutions, all these effects depend only on the number of particles present, not their identity.
Raoults Law The vapor pressure of a mixture of solvent and nonvolatile solute is proportional to the mole fraction of the solvent. PSolution= XSolvent * PoSolvent
Freezing point depression (ΔTf)= ΔTf= Kf*m Kf is the molal freezing point depression constant and the molal boiling point elevation constant, respectively. They are characteristic for each solvent. The unit is °C / mole.
boiling point elevation (ΔTb) = ΔTb= Kb*m Kb is the molal freezing point depression constant and the molal boiling point elevation constant, respectively. They are characteristic for each solvent. The unit is °C / mole.
Osmosis the movement of solvent molecules across a membrane. membranes are semi permiable. When osmosis occurs, a movement of solvent from the more dilute solution to the more concentrated solution takes places across the membrane.
reverse osmosis the movement of the solvent is reversed by applying pressure.
osmotic pressure = Π= M xR xT R is the gas constant, M the molar concentration, T the temperature
degree of dissosiation (van’tHoff factor i) i =Δ Tf(measured)/Δ Tf(calculated as a nonelectrolyte)
Created by: jsherm82