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KINETICS -REACTION RATES

KINETICS -REACTION RATES. AP Chem. RATE. D quantity / D time mol / L • s Average rate of product produced = negative average rate of reactant consumed Rate of a Rxn is always Positive Reaction rates are determined experimentally by measuring concentrations at various times. Rate Laws.

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KINETICS -REACTION RATES

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  1. KINETICS -REACTION RATES AP Chem

  2. RATE Dquantity / Dtime • mol / L• s • Average rate of product produced = negative average rate of reactant consumed • Rate of a Rxn is always Positive • Reaction rates are determined experimentally by measuring concentrations at various times

  3. Rate Laws • Equation that expresses the mathematical relationship between the rate of a rxn and the concentration of reactants • Include the specific rate constant “k” • k = numerical value that relates rxn rate & concentration of reactants at a given temp

  4. Specific Rate Constant (k) • k is unique for every rxn • k will NOT change with concentration • k will change with temperature • A large k value means that the reactants rapidly form products • Units can vary depending on situation • ie: L/mol•s, L2/mol2•s, 1/s

  5. General Form of Rate Laws General Reaction: aA + bB  products General Rate Law: Rate = k [A]m[B]n (m & n = reactions orders for A and B) Reaction Order defines how the rxn rate is affected by concentration of reactants

  6. Determining Reaction Order by Method of Initial Rates • Example:

  7. Integrated Rate Laws • Shows how concentration depends on time • Used for aA  products • Three types of Integrated Rate Laws: • Zero Order • First Order • Second Order

  8. Zero Order [A]t = -kt + [A]0 [A]0 = initial concentration [A]t = concentration at time t Half life – time required to reach half of original concentration t1/2 = [A]0 / 2k

  9. First Order ln[A]t = -kt + ln[A]0 ln[A]t – ln[A]0 = -kt ln([A]t/[A]0) = -kt t1/2 = 0.693/k

  10. Second Order 1/[A]t = kt + 1/[A]0 1/[A]t – 1/[A]0 = kt t1/2 = 1/k[A]0

  11. Determining Integrated Rate Law Order Graphically • You can determine the rxn order if given [A] and time by making a graph. • Plot: • [A] vs. time • ln[A] vs. time • 1/[A] vs. time (see which graph is linear)

  12. Zero Order • rate is constant; doesn’t change with concentration • plot of [A] vs. time = linear • Rate=k • -k=slope

  13. First Order • Concentration and rate are directly proportional • Plot of ln[A] vs. time = linear • Rate = k[A] • -k=slope

  14. Second Order • If [reactants] doubles, rate quadruples • Plot of 1/[A] vs. time = linear • Rate = k[A]2 • k=slope

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