Final answer:
The rate of chemical reactions in the PhET Reactions & Rates interactive increases with both concentration and temperature, due to more frequent and energetic collisions.
Step-by-step explanation:
In the PhET Reactions & Rates interactive, the rate of a chemical reaction is influenced by both the concentration of reactants and the temperature of the system. Two primary factors that can affect the rate at which reactions occur are the frequency and energy of collisions between the reactant molecules. Increasing the concentration of reactants generally leads to more frequent collisions, thereby increasing the rate of reaction.
Similarly, increasing the temperature typically raises the energy of particles, which increases the number of collisions and the proportion of collisions that have sufficient energy to overcome the activation energy barrier, thus leading to an increased rate of reaction.
When exploring the 'Many Collisions' tab in the simulation, you can observe that a higher concentration of reactants results in a more rapid formation of products because more particles are colliding with appropriate energy and orientation. Similarly, higher temperatures contribute to a faster reaction rate by providing more reactant particles with enough kinetic energy to react upon collision.
The collision model of chemical kinetics supports this by stating that reaction rates are influenced by the number of effective collisions—that is, collisions with proper orientation and enough energy to lead to product formation.