Chem Exam II

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gundrj
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69168
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Chem Exam II
Updated:
2011-02-27 01:00:08
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Chem Exam II
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Rate and Equilibrium
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  1. When determining and using initial rate laws there is
    • -require experiemntal data
    • -you are able to calculate reaction orders and calculate the value of the rate law
  2. The integrate rate law does what?
    -relates concentration to time
  3. First order reaction rate law?
    rate=k[A]
  4. First order integrated rate law?
    ln[A]t=-kt+ln[A]o as a linear equation
  5. Half-life is?
    Time require to concentration of the reactiant to be reduced by one half its original concentration.
  6. First order reaction half life equation?
    • t1/2=0.693/k
    • -for first order reactions the half-life is independant of the initial concentration
  7. Second order reaction rate law?
    rate=k[A]2
  8. Second order integrated rate law
    1/[A]t=kt-1/[A]o as a linear equation
  9. Second order reaction half-life equation?
    • t1/2=1/[A]ok
    • in the second order reation t1/2 depends on the intitial concentration.
  10. If the temperature increases...
    • Rate increases and
    • k increases
  11. Collision Theory
    To react, reactants must encounter eachother
  12. If we increase the number of successful collisions you...
    increase the rate
  13. If you increase the reactant concentration....
    you increase the number of collisions
  14. Succesful collisions require:
    • 1. collision must have sufficient energy
    • 2. collision must have reactants in the proper orientation
  15. Activation enegy is?
    Energy barrier between the reactants and the products.
  16. Activation energy graph
  17. The transition state is
    • short lived
    • where the intermediate is created and destroyed between the reactants and products
    • also called the activated complex
  18. What determines if the reactnat have sufficient E to form the transistion state
    • Energy (K.E.) of the reactant relative to the activation energy
    • -increase speed of K.E.
    • - lower the size of the barrier
  19. Frequency equation is
    f=e-Ea/RT
  20. If the frequency increases two things have happened
    • the temperature as been increased
    • the activation energy has decreased
  21. Molecular Orientation
    • not all collisions with the K.E. higher than the Ea with result in a trantisition state formation.
    • Bad collisions are caused from what and how the molecule is made.
  22. Arrhenius equation is
    k=Ae-Ea/RT
  23. A is the frequency factor and it is
    • specific to each reaction
    • depends on reactant geometry
    • is independant of temperature
  24. Uses of Arrhenius Equation
    • Graphical determination of Ea lnk=(-Ea/R)(1/T)+lnA
    • Determining k at various temperatures ln(k1/k2)=(Ea/R)(1/T2-1/T1)
    • When solving for either k make sure it is in the k1 position
  25. Reaction Mechanisms: Elementary steps
    • describe the actual interactions between reactants at the molecular level
    • descirve overall reactions as a series of steps; elementary steps: describe an actual collision
    • explains rate laws
  26. Molecularity
    classification of elementary steps based on the number of reactnatn in the collision
  27. Molecularity and Rate law
    for an elementary step; molecularity determines the rate law for one step at a time
  28. Molecularity determines the reaction order unimolecular rate law is
    rate=k[A]
  29. Molecularity determines the reaction order bimolecular rate law is
    • rate=k[A]2
    • rate=k[A][B]
  30. What is the rate determining step?
    • a specal step in a mechanism
    • slowest step in a mechanism
    • determines the rate of the overal reaction
  31. The rate law for the slowest step is what?
    • the rate law for the overall reaction
    • if the reaction occurs in one step the rate law correstongd to the overall reaction
  32. Determining reaction mechanisms by four steps
    • 1. based on experiemtnally determined rate law
    • 2. mechanisms consist only of elementary steps- plausible collisions
    • 3. one steop is rate determining-determines the overall rate law
    • 4. The sum of steps=the overall reaction
  33. Hints about reaction mechanisms
    • mechanisms tent to occur in a minimal amount of steps
    • reactions with a low overall reaction order (1 or 2) the initial step is usually the slowest
    • reactions with a fast initial step often have higher (3) overall reaction orders
    • reaction intermediates are usually in the slow reaction step(s)
  34. Catalyst is?
    a substance that decreases Ea, increases A in the Arrhenius equation
  35. Homogenous catalyst is?
    the catalyst and reactants are in the same phase
  36. heterogenous catalyst is?
    reactants and catalyst are in different phases
  37. A catalyst is a reaction does what to the mechanism?
    • lowers Ea by changing the transition state
    • changes the reaction mechanism
    • forms lower energy transition state
  38. Heterogenous cataysis usually happens by surface catalyzing
    • 1. adsorption: binding at the surface)
    • 2. migration: of the adsorbed reactants
    • 3. reaction at surface
    • 4. desorption: products are relaeased from binding at catalyst surface
  39. Enzymes
    speed up a reaction
  40. Proteins are
    amino acids
  41. Protein structures based off of primary structure and secondary and teritary structure the shape dictates the function and activity of the protein
    • primary structure-amino acid sequence
    • secondary and tertiary structure- define the overall shape of the protein, maintained by the amino acid interactions
  42. Enzyme mechanism process is a lock and key model
    • 1. reacnant substrate bind to the enzyme at the active sight
    • 2. forms enzyme sybstrate complez
    • 3. products are released
  43. Enzyme activity can be disruped by enzyme inhibitors by
    • 1. binding to the active site
    • 2. distoring the enzyme structure
  44. what is Dynamic equilibrium?
    • when forard and reverse reactions both occur at the same rate
    • both reactants and products are presents in a constant ratio but seldom equal amounts
  45. The product reaction ratio depends on
    • theormodynamics of the reaction
    • reaction conditions: temperature influence and pressure influence
  46. establishing equilibrium means that
    systems shift form initial conditions to establish the equilibrium ratio of the products to reactnat set by the reaction theromodynamics and the reactions conditions
  47. Kcis what?
    kc=[products]coefficients/[reactants]coefficients
  48. equilibrium of gases is Kp
    kp=(Pproducts)coefficients/(Preactants)coefficients
  49. The relationship equation between Kc and Kp
    Kp=Kc(RT)change in n
  50. evaluating equilibrium constants
    all k's are rations of prod/reactant
    if product is >reactant and if reactant is > product
    where does the equilibrium lie?
    • Product > reactant it lies to the right
    • reactant > product it lies to the left
  51. Heterogenous equilibrium when reactants and products are in multiple phases what phases aren't in k expressions?
    solids and liquids

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