MRD:01503126
Exercise one: H + H2 system
-On a potential energy surface diagram, how is the transition state mathematically defined? How can the transition state be identified, and how can it be distinguished from a local minimum of the potential energy surface?
The transition state would be local maxima on the local maxima of the minimum energy path. When the transition state is reached, since force is the derivative of potential energy, The force would be zero.
-Report your best estimate of the transition state position (rts) and explain your reasoning illustrating it with a “Internuclear Distances vs Time” plot for a relevant trajectory.
The best estimate of the transition state position exists when both the distances of AB and BC are 90.8 pm, the hydrogens have no momentum.
According to the Internuclear Distance vs Time plot, the distance remains unchanged, which corresponds to the zero forces acting on AB and BC hydrogens, so stationary nuclei at the transition state.
-Comment on how the mep and the trajectory you just calculated differ.
The difference between the two calculation types is whether the atomic motion is included or not. In mep the trajectory is a straight line since it does not take atomic motion into account. In dynamic the trajectory is more like a wavy curve, since it includes the atomic motion.
Complete the table above by adding the total energy, whether the trajectory is reactive or unreactive, and provide a plot of the trajectory and a small description for what happens along the trajectory. What can you conclude from the table?
Given the results you have obtained, how will Transition State Theory predictions for reaction rate values compare with experimental values?
The reaction rate predicted by Transition State Theory is overestimated comparing with the experimental values. Even if a hydrogen atom collides with an H2 molecule, it might bounce off and regenerate the reactants as an unreactive trajectory. The transition state theory does not take an unreactive trajectory into account so that the reaction rate is overestimated than the experimental values.
