Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

Which of the following is NOT a factor affecting reaction rates?

1. Time

2. Temperature

3. Concentration

4. Presence of a catalyst

The correct answer is: Time

Time is not considered a factor that affects reaction rates in the context of chemical kinetics. Instead, reaction rates are typically influenced by factors such as temperature, concentration of reactants, and the presence of a catalyst. Temperature affects the kinetic energy of molecules; higher temperatures increase the speed of molecular movement, leading to more frequent and energetic collisions, which can increase the rate of reaction. Concentration refers to the amount of reactants present; higher concentrations usually lead to a higher frequency of collisions between reactant molecules, thus speeding up the reaction. The presence of a catalyst provides an alternative reaction pathway with lower activation energy, facilitating a faster reaction without being consumed in the process. In contrast, time itself does not alter the inherent characteristics of the reactants or the conditions that influence how quickly the reaction occurs. It simply measures how long the reaction has been happening. As a result, time is not a direct factor in the rates of chemical reactions.