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Chemical Kinetics and Reaction Rates - General Chemistry

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  • What is chemical kinetics?
    The study of rates of chemical reactions, the factors that affect reaction rates, and the reaction mechanisms by which reactions occur.
  • What are reaction rates?
    How fast reactants are used to form products, relative to a unit of time.
  • What is a reaction mechanism?
    The sequence of steps that the molecule goes through to arrive at the final product.
  • How is reaction rate mathematically expressed for a generic reaction \(aA + bB \to cC + dD\)?
    Rate = -1/a Δ[A]/Δt = -1/b Δ[B]/Δt = 1/c Δ[C]/Δt = 1/d Δ[D]/Δt; rate is relative to mol reaction, so coefficients are included.
  • What does the rate constant (k) represent in the rate law?
    k is the rate constant for the reaction at one temperature, giving information on the reaction speed independent of concentration.
  • How is the rate law for a reaction with one reactant A expressed?
    Rate ∝ [A]; Rate = k[A], where k is the rate constant.
  • Can reaction orders be determined from the balanced chemical equation?
    No, the exponents (orders) in the rate law must be experimentally determined.
  • What does the order of a reaction indicate?
    The order for each reactant is the exponent for that reactant in the rate law; the overall order is the sum of all exponents.
  • How does doubling the concentration affect the rate for zero, first, and second order reactions?
    Zero order: no change; First order: rate doubles; Second order: rate quadruples (x4).
  • What factors affect reaction rates?
    Nature of reactants, concentration of reactants, temperature, and presence of a catalyst.
  • What is the effect of increasing surface area on reaction rate?
    More surface area exposes more molecules to reactants, increasing the reaction rate.
  • How is the rate law for a reaction with two reactants A and B expressed?
    Rate = k[A]^x[B]^y, where x and y are the orders with respect to A and B, determined experimentally.
  • What is the method of initial rates used for?
    To determine the reaction orders and rate constant by measuring initial rates at different initial concentrations.
  • What is the integrated rate law for a first order reaction?
    ln([A]_0/[A]) = akt, where [A]_0 is initial concentration, [A] is concentration at time t, a is stoichiometric coefficient, and k is rate constant.
  • What is the half-life expression for a first order reaction?
    t_1/2 = (ln 2) / (a k), independent of initial concentration.
  • What is the integrated rate law for a second order reaction?
    1/[A] - 1/[A]_0 = a k t.
  • How does the half-life of a second order reaction depend on initial concentration?
    t_1/2 = 1 / (a k [A]_0); half-life depends inversely on initial concentration.
  • What is the integrated rate law for a zeroth order reaction?
    [A] = [A]_0 - a k t.
  • How does the half-life of a zeroth order reaction depend on initial concentration?
    t_1/2 = [A]_0 / (2 a k); half-life depends directly on initial concentration.
  • How can reaction order be determined graphically?
    First order: ln[A] vs. time is linear; Second order: 1/[A] vs. time is linear; Zeroth order: [A] vs. time is linear.
  • What is collision theory?
    Molecules must collide with sufficient energy and proper orientation for a reaction to occur.
  • What is the transition state in a reaction?
    A high energy intermediate formed between reactants and products; energy required to reach it is the activation energy.
  • What is the Arrhenius equation?
    k = A e^{-Ea/(RT)}, relating rate constant k to activation energy Ea, temperature T, and frequency factor A.
  • How does temperature affect reaction rate according to Arrhenius equation?
    Increasing temperature increases k and reaction rate, often doubling rate for every 10°C increase near room temperature.
  • What is the rate-determining step in a reaction mechanism?
    The slowest step with the highest activation energy that controls the overall reaction rate.
  • What is the difference between homogeneous and heterogeneous catalysts?
    Homogeneous catalysts are in the same phase as reactants; heterogeneous catalysts are in a different phase, usually solid.
  • What role do enzymes play in biochemical reactions?
    Enzymes are biological catalysts that are highly specific and efficient, often catalyzing reactions under mild conditions.