Visualizing the Transition State: A Hands-On Approach to the Arrhenius Equation

An exercise is presented in which the kinetics of the irreversible "reaction" of pennies in the heads-up state to pennies in the tails-up state is simulated by a hands-on, Monte Carlo approach. In addition, the exercise incorporates a second simulation in which the irreversible "reaction" of dice with a red face uppermost to a blue face uppermost is conducted. The transition states of the reactions are assumed to be a penny that is in the process of being flipped or a die in the process of being rolled, respectively. Data collected by students who perform these simulations show that both "reactions" follow first-order decay kinetics. Arrhenius plots from these data yield activation energies comparable to assigned values and pre-exponential factors close to what would be expected based on the probability of a "reactant" achieving the correct orientation for conversion into "product". A comparison of the values obtained for the pre-exponential factors for the different simulations allows students to semi-quantitatively discuss the orientational requirement that is contained within this factor. (Contains 3 figures.)