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Reaction Rates and Rate Laws: Flashcards

Revise reaction rates, factors affecting rate, rate laws, orders, units of k and half-life.

10 cardsIntermediate

10 cards

  1. Question
    What is the rate of a reaction?
    Answer

    The change in concentration of a reactant or product per unit time, usually in M/s.

  2. Question
    Name four factors that increase the rate of a reaction.
    Answer

    Higher concentration (or pressure), higher temperature, larger surface area, a catalyst.

  3. Question
    In rate = k[A]²[B], what are the orders?
    Answer

    Second order in A, first order in B, third order overall.

  4. Question
    How are reaction orders found?
    Answer

    By experiment (e.g. the method of initial rates), not from the balanced equation.

  5. Question
    A reaction is second order in A. [A] is doubled. What happens to the rate?
    Answer

    It is multiplied by 2² = 4.

  6. Question
    Units of k for a first-order reaction?
    Answer

    s⁻¹

  7. Question
    Units of k for a second-order reaction?
    Answer

    M⁻¹ s⁻¹ (because M s⁻¹ ÷ M² = M⁻¹ s⁻¹)

  8. Question
    Half-life of a first-order reaction?
    Answer

    t1/2=0.693kt_{1/2} = \dfrac{0.693}{k}, independent of the starting concentration.

  9. Question
    What fraction of a first-order reactant remains after 3 half-lives?
    Answer

    (½)³ = ⅛ = 12.5%

  10. Question
    In 2N₂O₅ → 4NO₂ + O₂, how does the rate of NO₂ formation compare with the rate of N₂O₅ loss?
    Answer

    NO₂ forms twice as fast (4 mol NO₂ per 2 mol N₂O₅).