Ch 12

Cards (12)

  • The sum of the exponents in the rate law equation.
    Rate = k[A]n[B]m
    Overall reaction order = n+ m
    • Differential Rate Law(rate law) –shows how reaction rate depends on concentrations.
    • Integrated Rate Law–shows how the concentration of reactants varies as a function of time.
  • How do exponents (orders) in rate laws compare to coefficients in balanced equations?
    They are not related.
    Why?
    The balanced chemical equation is the sum of all elementary steps and the rate law depends on the slowest step only.
  • Some chemical species are formed and consumed during the course of a chemical reaction. Thus they are never seen as a product in the overall balanced reaction. These species are known as intermediate of reaction.
  • Most chemical reactions do not proceed as suggested by the balanced chemical reaction; instead they occur by a series of elementary steps, called themechanism of reactions.
    • Number of species that must collide to produce the reaction represented by an elementary step
    •Unimolecular–elementary step involving one molecule
    •Bimolecular–elementary step involving the collision of two chemical species 
    •Termolecular–elementary step involving the collision of three chemical species.  Very rare.
    •The rate law can be written from the rate limiting step (the slowest one).
  • •Molecules must collide for reaction to occur.
    •Main Factors:
    •Activation energy, Ea
    •Temperature
    •Molecular orientations
  • Activation Energy, Ea
    •Energy that must be overcome to produce a chemical reaction.
    •Energy required to break the chemical bonds of the reactants; so that elements can re-organize to make the products.
  • Heterogeneous Catalyst
    •Most often involves gaseous reactants being adsorbed on the surface of a solid catalyst.
    •Adsorption –collection of one substance on the surface of another substance.
  • Homogeneous Catalysis
    •Exists in the same phase as the reacting molecules
    •Consider the catalytic behaviorof nitric oxide toward ozone
    •NO catalyzesozone production in the troposphere
    •In the lower atmosphere, NO is produced in any high-temperature combustion process in the presence of N2
  • Homogeneous catalysts are those which exist in the same phase (gas or liquid ) as the reactants, while heterogeneous catalysts are not in the same phase as the reactants.
  • Intermediate = formed & consumed
    Catalyst = added