Question

Why do kinetic energy and ionic repulsion/ attraction influence the reaction rate ?

Answer 1

In the picture above, the electron state is said to be in bonding state because it allows for the two atoms to bind together to form an equilibrium arrangement (this corresponds to the minimum in that curve). Usually in such bonding state, most electrons are found in the volume in between the two nuclei. That's why they can bring those nuclei closer. However, if the two nuclei gets too close past its equilibrium, the repulsive force between them will start to dominate and at some point (when the curve cross the x axis) they will break. As is mentioned in the beginning, different electron density can lead to different potential curve. One worth to mention is the so-called repulsive state where there is small chance to find electrons in the region between the nuclei so that there is no way the repulsive force between them can be compensated. The form of the corresponding potential curve exhibits a monotonically decreasing function (thus, no minimum/equilibrium) toward an asymptotic value when the internuclear distance approaches infinity.

During a molecular collision, molecules must also possess a minimum amount of kinetic energy for an effective collision to occur. This energy varies for each reaction, and is known as the activation energy (Ea). The rate of reaction therefore depends on the activation energy; a higher activation energy means that fewer molecules will have sufficient energy to undergo an effective collision.

Ionic strength is a measure of the total dissolved salt ions in solution. Ions in solution are attracted to other ions of the opposite charge, and are shielded by this attraction. For example, let’s say one of the reactants in a reaction involving two reactants has a positive charge. A positively charged ion will tend to be surrounded by negative ions in solution — here we are speaking of ions that don’t have anything to do with the reaction but are also dissolved in the solution. This would tend to reduce the ability of the ion to encounter the other reactant, and therefore suppress the rate of reaction.

You would need to know the full reaction mechanism and rate constants of the rate-limiting steps of a specific reaction to come up with a final answer, since charged intermediates of a multi-step reaction would be similarly effected by ions in the solution.