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Activation energy and the Arrhenius equation Knowledge-Based Practice

Chemistry · Chemical Kinetics · Chemistry · Reaction Mechanisms & Catalysis

5 Chemistry practice questions on Activation energy and the Arrhenius equation. Questions that assess core concepts and understanding.

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Questions

  1. 1.

    In terms of the Arrhenius equation, how does a catalyst increase the rate of a chemical reaction at a constant temperature?

    • A) By increasing the temperature, thereby raising the average kinetic energy of the reacting particles
    • B) By increasing the pre-exponential factor (AA) through a large rise in total collision frequency
    • C) By lowering the activation energy (EaE_{\text{a}}), which increases the value of the exponential term e−Ea/(RT)e^{-E_{\text{a}}/(RT)}
    • D) By increasing the reaction enthalpy (ΔH\Delta H), which thermodynamically favors product formation
  2. 2.

    In the Arrhenius equation, k=Ae−Ea/(RT)k = A e^{-E_{\text{a}}/(RT)}, what does the pre-exponential factor (AA) primarily account for according to collision theory?

    • A) The fraction of molecular collisions that possess kinetic energy equal to or greater than the activation energy
    • B) The total enthalpy change of the reaction and the thermodynamic favorability of forming products
    • C) The frequency of molecular collisions and the probability that colliding particles possess the correct steric orientation
    • D) The reduction in the energy barrier caused by the presence of a homogeneous catalyst
  3. 3.

    According to the Arrhenius equation, how does the magnitude of the activation energy (EaE_{\text{a}}) influence the temperature sensitivity of the rate constant for a chemical reaction?

    • A) A reaction with a lower EaE_{\text{a}} experiences a greater fractional increase in its rate constant for a given temperature increase.
    • B) A reaction with a higher EaE_{\text{a}} experiences a greater fractional increase in its rate constant for a given temperature increase.
    • C) The fractional increase in the rate constant for a given temperature increase is identical regardless of the magnitude of EaE_{\text{a}}.
    • D) A reaction with a higher EaE_{\text{a}} experiences a decrease in its rate constant when the temperature is raised.
  4. 4.

    In the Arrhenius equation, k=Ae−Ea/(RT)k = A e^{-E_{\text{a}}/(RT)}, what physical quantity is represented by the exponential term e−Ea/(RT)e^{-E_{\text{a}}/(RT)}?

    • A) The fraction of molecular collisions with kinetic energy equal to or greater than the activation energy
    • B) The total frequency of collisions occurring between reactant molecules per unit volume
    • C) The fraction of collisions that occur with the geometrically correct steric orientation
    • D) The net enthalpy change between the ground state reactants and the transition state
  5. 5.

    According to the Arrhenius equation, how does an increase in temperature affect the rate constant, and which graphical representation yields a linear plot with a slope of −EaR-\frac{E_{\text{a}}}{R}?

    • A) The rate constant decreases; a plot of kk versus TT
    • B) The rate constant increases; a plot of ln⁡k\ln k versus TT
    • C) The rate constant decreases; a plot of ln⁡k\ln k versus 1T\frac{1}{T}
    • D) The rate constant increases; a plot of ln⁡k\ln k versus 1T\frac{1}{T}

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