Study guide for Exam 2 of Gen Chem 2
Study guide for Exam 2 of Gen Chem 2 chem 10061-001
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This 4 page Study Guide was uploaded by Matthew Goetz on Sunday March 13, 2016. The Study Guide belongs to chem 10061-001 at Kent State University taught by David bowers in Summer 2015. Since its upload, it has received 37 views. For similar materials see general chemistry 2 in Chemistry at Kent State University.
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Date Created: 03/13/16
Gen Chem Study Guide 2 A majority of this test will focus on solution properties. To determine them, we will use 6 base equations: Molality = (moles of solute/kg of solvent) Parts by mass = (mass of solute/total mass) Parts by volume = (volume of solute/ total volume) Mole fraction = (moles of solute/ total moles) Parts per million = (mass of solute/total mass of solution) x 100,000 These equations may be used to calculate colligative properties. These are changes that occur in a solvent when a solute is added. They are vapor pressure reduction, boiling point elevation, freezing point depression, and a change in osmotic pressure. These properties depend on the # of solute particles dissolved. These properties occur because: Solute particles in the solution raise entropy, which reduces vapor pressure. Solute particles in solution make it harder for solutions to change phase. Nonvolatile nonelectrolyte solutions These experience all of the colligative properties that were described above. These don’t involve ionic solutes, so they don’t dissolve. These experience a vapor pressure reduction, expressed by this equation: X is the mole fraction Psolv is the vapor pressure of pure solvent. These experience boiling point elevation, expressed by this equation: Kb is a given constant. M is the molality of the solution. These experience freezing point depression, expressed by this equation: The parts of this equation are the same as the boiling point elevation. The osmotic pressure of these solutions also changes, expressed by: π = mrt M is the molarity. R is a constant .08206 T is the temperature of kelvin. The colligative properties of volatile, nonelectrolyte solutions: Depress the volatility and vapor pressure of each other. Strong electrolyte solutions: Due to dissociation, one must multiply equations by the Van’t Hoff factor. This is the factor that states how many moles will be present after ionic dissociation. The equations are the same for this, just multiplied by the vant hoff factor. In kinetics, (molarity x seconds) is the speed of reactions. Chemical kinetics: The study of reaction rates. Reaction rates may be sped up or slowed down by controlling: Concentration of solute Temperature The presence of a catalyst Physical state of the solution Reaction rate = (Change in concentration/ change in time) Reactions slow over time as products form and impede the colliding of reactants. Therefore, the reactions are fastest when they first start. • For reactions involving coefficients, use the equation: aA + bB yields cC + dD. Rate law expression: For instantaneous rates, Rate = k[A]^x[B]^y k is the rate constant x and y are the orders of reaction with respect to the reactants Rate law only includes reactions!!! Reaction orders are determined by experiment. First order reactions are when the rate of A is directly proportional to the concentration. So, if A doubles, then the concentration doubles as well. Second order reactions are when the rate is the square of the concentration. So, if A doubles, then the concentration quadruples. Or, if A triples, then the concentration is multiplied by 9. Zero order reactions are when the Rate has no effect on the concentration. To determine the rate constant K: k = (rate/ [A]^m[B]^n) The units for K will vary though depending on the equation. Zero order reactions use the unit mol/Lxs First order reactions use the unit 1/s Second order reactions use the unit L/molxs Integrated rate laws: Show how time and rate are related. Halflife: Time it takes for a concentration to halve. This is important in first order reactions. In first order reactions the concentration doesn’t affect halflife though. Halflife may be solved using the equation: Collision theory: Reaction rate in relation to the # of solute particles. This theory is due to the fact that particles must collide to react. This is the basis of rate laws. If concentration increases then more collisions may occur, so the reaction will speed up. A collision that yields a product is called an effective collision. This requires particles to collide in the correct orientation and with enough energy to overcome the activation energy. This is important because many collisions of particles don’t result in formation of a product. Temperature is also an important factor, for it increases kinetic energy in a system. For most reactions that occur at room temperature: Increasing 10 degrees Celsius doubles the rate. This is a rule of thumb. The Clausius Clapeyron equation may be used to calculate the activation energy if you know the rate constant at 2 different temperatures. Structures of molecules and their orientations affect their reactivity. A = the collision frequency factor. A =pZ. P = orientation probability factor. Z = collision frequency. P is high for individual atoms. Transition state theory: Between reactants and products, there is a transitional species that forms. This is a high energy, unstable species that only exists for a brief instant. Such a brief existence that they have never been isolated. These have higher coordination numbers due to partial bonds that form.
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