Explain, in terms of collision theory, how and why a reaction’s rate changes as the reaction progresses.
It seems obvious to me that if you put more molecules together there must be a better and increasing chance that they will bump into each other. Right?
yep
In collision theory, the rate of a reaction depends on the number of effective collisions between reacting particles. Effective collisions occur when colliding particles have sufficient energy and proper orientation to overcome the activation energy barrier and lead to a successful reaction.
As a reaction progresses, several factors can cause changes in the reaction rate:
1. Reactant concentrations: According to collision theory, an increase in reactant concentration leads to an increase in the number of collisions, thus increasing the rate of the reaction. This is because a higher concentration of particles means a higher likelihood of colliding and increasing the chance of effective collisions.
2. Temperature: Increasing the temperature of a reaction increases the kinetic energy of the particles. This higher energy results in more frequent and energetic collisions, leading to an increased rate of successful collisions and a faster reaction rate.
3. Surface area: For reactions involving solid reactants, an increase in surface area can enhance the rate. This is because a larger surface area provides more exposed particles for collisions, increasing the chances of effective collisions and therefore accelerating the reaction rate.
4. Catalysts: Catalysts are substances that can speed up a reaction without being consumed in the process. They work by providing an alternative reaction pathway with a lower activation energy. By lowering the energy barrier, more particles will have enough energy to overcome it, leading to a higher rate of effective collisions and an accelerated reaction rate.
In summary, changes in reactant concentrations, temperature, surface area, and the presence of catalysts can all impact the rate of a reaction. Increasing these factors generally increases the frequency and/or effectiveness of collisions between reacting particles, leading to a faster reaction rate as the reaction progresses.