A detailed molecular understanding of heterogeneously catalyzed reactions can be obtained by probing the role of internal energy in the observed dynamics of the reaction. Focusing on the activation of methane and on catalytic oxidation on platinum surfaces, we have used this approach over the past several years to learn about the dynamics of surface reactions. In the case of catalytic oxidation, we have used direct infrared absorption spectroscopy to measure the internal state distribution of the CO₂ product of the oxidation of CO, ethylene, and methanol on the platinum surface. We have found that the product internal state distribution depends strongly on the reaction conditions and the reactants involved, providing information about the transition state for the formation of product CO₂. For the activation of methane on the platinum surface, we have examined the effect of internal excitation of the methane reactant on its subsequent dissociative adsorption probability. We have found that the dissociative adsorption probability is directly affected by the internal excitation of the reactant methane. These experimental results and their interpretation will be discussed.