Video Transcript
Which of the following factors does not affect the rate of a chemical reaction? (A) Catalysts, (B) surface area, (C) temperature, (D) concentration, or (E) color of
the reactants.
A chemical reaction can happen when particles collide with each other. This figure shows how reactant particles turn into a product when they undergo a
successful collision. The rate of a chemical reaction is proportional to the frequency of successful
collisions between reactant particles. The rate of a reaction measures how reactant or product concentrations change over
time. If the frequency of successful collisions between reactant particles increases, the
rate of the chemical reaction will also increase.
Since this question is asking us which of the factors does not affect the rate of a
reaction, we must identify the answer choice that does not change the frequency of
successful collisions. Let’s have a look at our answer choices.
Answer choice (A), catalysts are substances that increase the rate of a reaction by
lowering the minimum amount of energy needed for a successful collision. Not every particle collision is successful at resulting in a reaction. One factor that impacts whether a particle collision will be successful or not is if
the particles collide with enough energy. For a reaction to actually happen, the particle collisions must overcome an amount of
energy specific to a reaction. With a catalyst, the amount of energy required for the reaction to occur is
lowered. Catalysts do affect the rate of a reaction by increasing the chances of successful
collisions. Therefore, answer choice (A) is not the correct answer.
Answer choice (B) is surface area. For solid reactants, the size of the pieces alters the surface area. When a solid reactant is in a large chunk, its surface area is low and only particles
on the outer edge of the solid are available to react initially. But if the large chunk is ground into smaller pieces, like a powder, the higher
surface area makes more particles available to collide. Surface area can affect the rate of a reaction, and so it is not the answer to this
question.
The temperature of the particles, answer choice (C), is another factor of a chemical
reaction. When the temperature is raised, the particles move more quickly and thus have more
energy and likelihood to collide. Since temperature can affect the rate of a reaction, we can eliminate answer choice
(C).
Answer choice (D) is concentration. When the concentration of reactants is increased, there are more total particles per
volume and thus more opportunities for successful collisions. Concentration can affect the rate of a reaction, and so we can eliminate answer
choice (D).
Answer choice (E) is the color the of reactants. The color of the reactants does not impact the frequency of successful collisions
between them. Answer choice (E) is the correct answer.
So, the factor that does not affect the rate of a chemical reaction is answer choice
(E) color of the reactants.
