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EK Chem 2

Gases, Kinetics, and Chemical Equilibrium

QuestionAnswer
STP standard temperature and pressure: 0 degrees C and 1 atm; where the avg distance btw gas molecules is 35 angstroms
mean free path distance traveled by a gas molecule between collisions
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
kinetic molecular theory illustrates the 4 characteristics of an ideal gas
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
Ideal gas law PV = nRT
Gas constant, R = 0.08205 L atm / K mol = 8.314 J/ mol K
Charles law at CONSTANT PRESSURE, volume of gas is proportional to T
Boyle's law at CONSTANT TEMPERATURE, volume of gas is inversely proportional to P
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
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
Dalton's law total pressure exerted by a gaseous mixture is the sum of the partial pressure of each of its gases
K.E.average = 3/2 R*T average translational KE is proportional to temperature
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
effusion spreading of a gas from high pressure to low pressure through a pinhole, rate can be predicted by Graham's law
diffusion spreading of one gas into another gas/empty space, rate of diffusion can be approximated by Graham's law
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
real gases deviation in terms of volume Vreal > Videal molecules do have a volume so their volume must be added to the ideal volume
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
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
rate constant defined by the Arrhenius equation k = Aexp(-Ea/RT) where Ea is the activation energy depends on pressure, catalysts and temperature
rate of rxn ____ with temperature because _____ increases; bc more collisions with sufficient relative kinetic energy occurs each second
overall order of rxn sum of the exponents of each respective reactant
rate determining step the rate of the slowest elementary step that determines the rate of the overall reaction
catalyst substance that increase the rate of rxn w/o being consumed or permanently altered, can lower activation energy or increase steric factor
heterogenous catalyst catalyst in a different phase than reactants or products
homogenous catalyst catalyst in the same phase as reactants and products
chemical equilibrium where the forward rxn rate equals the reverse rxn rate, no change in conc of products or reactants
equilibrium constant K, constant to describe equilibrium, depends on temperature only = products^coeff/reactants^coeff
reaction quotient Q = products^coeff/reactants^coeff this is used to predict direction in which rxn will proceed
if Q = K, then.. rxn is at equilibrium
if Q > K, then... reverse rxn rate will be greater in order to shift rxn to equilibrium
if Q < K, then... forward rxn rate will dominate in order to shift rxn to equilibrium
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)
Created by: miniangel918