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Chemistry II Notes – Week 3Ch 14Raoult’s Lawo Two liquids mixed will both affect the vapor pressureAdd together both liquid’s individual vapor pressureo If the two liquids have strong attractions to each other the vapor pressure will be smaller than expectedBoiling point elevationo Directly proportional to the molal concentration of solute particles o BPsolution-BPsolute=ΔTb=m·kbWhere kb is a constanto Boiling point of a solution is higher than the boiling point of the pure solventFreezing Point Depressiono The freezing point for a solution is lower than it is pure solvent o Like boiling point elevation, it is directly proportional to the molal concentration of solute particleso Same equation except with kf constantOsmosiso Flow of water from low concentration to high concentration of solution o Separated by semipermeable membrane and only the solvent moves o Often thought of as the flow of water against gravityOsmotic pressureo Amount of pressure needed to keep osmotic flow from taking place o Proportional to molarity of solute particlesMeaning if there are moles of solute form the water to flow towards then the osmotic pressure will be highero Also based off of Van’t Hoff factorsLarger Van’t Hoff factors equal larger osmotic pressureo П=MRTVan’t Hoff Factoro Ratio of moles of solute particles to moles of formula units dissolved o Always less than theoretical values because the ions may dissociate but they may be still be close enough to each other to not be considered fully dissociatedCh 15: Chemical KineticsReaction rateo Speed of a chemical reaction o Important to be able to control the speed of a chemical reaction o 3 things that effect reaction rateConcentration of reactantsGreater reaction rate with greater concentrationReaction happens when particles collide productivelyIncreased temperature
The particles move faster at a higher temperature so they are more likely to collideIf they are moving faster they are also more likely to have high enough activation energy to cause a reaction if they do collideGases are the exception – they are less likely to react if they are at a higher temperatureReactant orientationCan cause a change in what is produced when they collideB + A-A = B-A-AB + A-X = B-A-X or B-X-ARateo How much a quantity changes during a period of time o Rate=–Δ[H2]/Δt(where the reactant is Hydrogen)o You can graph the rate of the reaction on a graph as a curveAverage rateo Change in measured concentrations in any particular time period o As the reaction continues, the concentration of reactant decreases causing the reaction to slow down Instantaneous Rateo Change in concentration at any one particular timeSlope at one point on the cure – tangent lineReaction Rate and Stoichiometryo The coefficients of the elements in the reaction’s equation help indicate the rate of change for each elemento The change in concentration of each substance is multiplied by 1/coefficient Monitoring a reaction continuously o Need to know Total pressurePolarimetrySpectrophotometryRate lawo The rate of a reaction is directly proportional to the concentration of each reactant raised to a powero For the reaction aA + bB = productsn and m are order for each reactantk is the rate constantrate = k [A]n [B]mReaction ordero Coefficient in front of the element o Sum of the exponents on the reactantsOverall order of the reactionZero ordero One reactant decomposing o Rate of reaction will not change with concentration changeFirst order
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