Chemistry Clarity · chemistryclarity.com

Activation Energy and Catalysts: Flashcards

Revise activation energy, energy profiles, the Maxwell–Boltzmann distribution, the Arrhenius equation and catalysts.

10 cardsIntermediate

10 cards

  1. Question
    What is activation energy, Ea?
    Answer

    The minimum energy colliding particles need in order to react.

  2. Question
    What two conditions must a collision meet to cause a reaction?
    Answer

    Energy at least equal to Ea, and a suitable orientation.

  3. Question
    What is the transition state?
    Answer

    The highest-energy arrangement on the energy profile, partway between reactants and products.

  4. Question
    Why does a small rise in temperature greatly increase the rate?
    Answer

    The fraction of molecules with energy ≥ Ea (the area beyond Ea on the Maxwell–Boltzmann curve) increases sharply.

  5. Question
    Write the Arrhenius equation.
    Answer

    k=A e−Ea/RTk = A\, e^{-E_\text{a}/RT}, with R=8.314R = 8.314 J/(mol·K) and T in kelvin

  6. Question
    Two-temperature form of the Arrhenius equation?
    Answer

    ln⁡k2k1=EaR(1T1−1T2)\ln\dfrac{k_2}{k_1} = \dfrac{E_\text{a}}{R}\left(\dfrac{1}{T_1} - \dfrac{1}{T_2}\right)

  7. Question
    How does a catalyst increase the rate?
    Answer

    It provides an alternative pathway with a lower activation energy, and is regenerated at the end.

  8. Question
    Does a catalyst change ΔH or K?
    Answer

    No. It lowers Ea for both directions equally, so ΔH, the equilibrium position and K are unchanged.

  9. Question
    Ea (forward) = 120 kJ/mol and ΔH = −40 kJ/mol. What is Ea (reverse)?
    Answer

    120 kJ/mol + 40 kJ/mol = 160 kJ/mol

  10. Question
    Homogeneous vs heterogeneous catalyst?
    Answer

    Homogeneous: same phase as the reactants. Heterogeneous: different phase, usually a solid surface (e.g. iron, platinum).