Gases, Kinetics, and Chemical Equilibrium
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| STP | standard temperature and pressure: 0 degrees C and 1 atm; where the avg distance btw gas molecules is 35 angstroms
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| mean free path | distance traveled by a gas molecule between collisions
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| typical gas... | loose collection of weakly attracted atoms or molecules moving rapidly in random reactions, miscible with each other (mix regardless of polarity) but over time heavier gases will settle at low T's
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| kinetic molecular theory | illustrates the 4 characteristics of an ideal gas
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| Rules for an ideal gas | 1. gas molecules have ZERO VOLUME
2. gas molecules exert NO FORCES other than repulsive forces due to collisions
3. gas molecules make completely ELASTIC COLLISIONS
4. average KE of gas molecules is directly proportional to T of gas
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| Ideal gas law | PV = nRT
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| Gas constant, R | = 0.08205 L atm / K mol = 8.314 J/ mol K
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| Charles law | at CONSTANT PRESSURE, volume of gas is proportional to T
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| Boyle's law | at CONSTANT TEMPERATURE, volume of gas is inversely proportional to P
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| standard molar volume | 22.4 L; this is the volume that all gases behaving ideally will occupy if they have the same temperature, pressure, and number of molecules AT STP
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| partial pressure | pressure the gas would produce in the container by itself
Pa = Xa * Ptotal where Pa is the partial pressure and Xa is the mole fraction
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| Dalton's law | total pressure exerted by a gaseous mixture is the sum of the partial pressure of each of its gases
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| K.E.average | = 3/2 R*T
average translational KE is proportional to temperature
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| Graham's law | describes the ratio of the Vrms of 2 gases in a homogeneous mixture--
v1/v2 = sqrt(m2)/sqrt(m1)
avg speed of pure gas is inversely proportional to the sqrt of the mass of pure gas
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| effusion | spreading of a gas from high pressure to low pressure through a pinhole, rate can be predicted by Graham's law
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| diffusion | spreading of one gas into another gas/empty space, rate of diffusion can be approximated by Graham's law
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| real gases deviate from ideal behavior.. how and when | when molecules are close together, modeled by van der wals equation which approimxates the real P and V of a gas
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| real gases deviation in terms of volume | Vreal > Videal
molecules do have a volume so their volume must be added to the ideal volume
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| real gases deviation in terms of pressure | Preal < Pideal
bc molecules DO exhibit forces (attractive when far apart) on each other - so this will pull the gas molecules inward toward the center of gas before colliding with the container walls --> strike the wall w/ less force then predicted
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| collision model requirements | 1. relative kinetic energies of the colliding molecules must reach a threshold energy (activation energy)
2. colliding molecules must have the proper spatial orientation
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| rate constant defined by the Arrhenius equation | k = Aexp(-Ea/RT) where Ea is the activation energy
depends on pressure, catalysts and temperature
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| rate of rxn ____ with temperature because _____ | increases; bc more collisions with sufficient relative kinetic energy occurs each second
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| overall order of rxn | sum of the exponents of each respective reactant
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| rate determining step | the rate of the slowest elementary step that determines the rate of the overall reaction
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| catalyst | substance that increase the rate of rxn w/o being consumed or permanently altered, can lower activation energy or increase steric factor
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| heterogenous catalyst | catalyst in a different phase than reactants or products
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| homogenous catalyst | catalyst in the same phase as reactants and products
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| chemical equilibrium | where the forward rxn rate equals the reverse rxn rate, no change in conc of products or reactants
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| equilibrium constant | K, constant to describe equilibrium, depends on temperature only
= products^coeff/reactants^coeff
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| reaction quotient | Q = products^coeff/reactants^coeff
this is used to predict direction in which rxn will proceed
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| if Q = K, then.. | rxn is at equilibrium
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| if Q > K, then... | reverse rxn rate will be greater in order to shift rxn to equilibrium
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| if Q < K, then... | forward rxn rate will dominate in order to shift rxn to equilibrium
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| Le Chatelier's principle | when a system at equilibrium is stressed, the system will shift in a direction that will reduce that stress (removal of product/reactant, changing of pressure, heating or cooling)
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