Question

question 24 of 32
which of the following tends to decrease the rate of a chemical reaction?

a. using a less concentrated reaction mixture

b. heating the reaction mixture

c. using larger particles of the solid reactant

d. adding a catalyst to the mixture

Explanation:

• Option A: A less concentrated reaction mixture has fewer reactant particles per unit volume, so the frequency of collisions between reactant particles decreases, which tends to decrease the reaction rate.
• Option B: Heating a reaction mixture increases the kinetic energy of particles, leading to more frequent and energetic collisions, thus increasing the reaction rate.
• Option C: Larger particles of a solid reactant have a smaller surface area available for reaction. With less surface area, the frequency of collisions between reactant particles (solid and other reactants) decreases, which decreases the reaction rate.
• Option D: A catalyst lowers the activation energy of a reaction, making it easier for the reaction to occur, thus increasing the reaction rate.

So both A and C tend to decrease the reaction rate. But if we consider the options, let's analyze again:

For A: Concentration affects reaction rate. Lower concentration means fewer collisions, so rate decreases.

For C: Larger solid particles have less surface area. Surface area affects reaction rate (for heterogeneous reactions with solids). Less surface area means fewer collisions at the surface, so rate decreases.

If we have to choose the most probable or common ones, but the question is which "tends to decrease", so both A and C are correct? Wait, maybe the question is from a context where maybe multiple correct, but let's check the options again.

Wait, maybe the original question's options: Let's re-express:

A: Less concentrated mixture: lower concentration → lower collision frequency → lower rate. Correct for decreasing rate.

B: Heating: increases rate. Incorrect.

C: Larger solid particles: smaller surface area → lower collision frequency at surface → lower rate. Correct for decreasing rate.

D: Catalyst: increases rate. Incorrect.

So both A and C are correct. But maybe in the question's context, maybe the options are such that A and C are correct. But let's check the options again.

Wait, the user's question is "Which of the following tends to decrease the rate of a chemical reaction?" with options A, B, C, D.

So the correct options are A and C. But maybe the question expects multiple answers? Or maybe I made a mistake.

Wait, let's recall factors affecting reaction rate:

• Concentration: higher concentration → higher rate (more collisions). So lower concentration (less concentrated) → lower rate. So A is correct.

• Temperature: higher temperature → higher rate (more energetic collisions). So heating (increasing temperature) → higher rate. So B is incorrect.

• Surface area (for solids): smaller particles (larger surface area) → higher rate (more collisions at surface). So larger particles (smaller surface area) → lower rate. So C is correct.

• Catalyst: increases rate by lowering activation energy. So D is incorrect.

So both A and C are correct. But maybe the question has multiple correct options. So the answer would be A and C. But let's check the options again.

Wait, the options are:

A. Using a less concentrated reaction mixture

B. Heating the reaction mixture

C. Using larger particles of the solid reactant

D. Adding a catalyst to the mixture

So the correct options are A and C.

Answer:

A. Using a less concentrated reaction mixture, C. Using larger particles of the solid reactant