Which of the following factors does NOT affect the rate of a chemical reaction?

1. Analyze the question We need the one factor that does not influence how fast a reaction goes.

2. Explain the concept According to collision theory, a reaction occurs when particles collide with enough energy (activation energy) and the right orientation. The rate depends on how often and how effectively particles collide. The main factors are:

• Concentration of reactants (or pressure for gases): more particles in a given volume means more frequent collisions.
• Temperature: particles move faster and more of them have energy at or above the activation energy.
• Catalyst: provides an alternative pathway with lower activation energy.
• Surface area of solid reactants: more exposed surface means more collisions.
• Light, for photochemical reactions.

3. Step-by-step solution

• A. Concentration of reactants: affects the rate, since higher concentration gives more collisions.
• B. Presence of a catalyst: affects the rate by lowering activation energy.
• C. Molecular weight of products: the mass of the products does not change how often reactant particles collide or how much energy they have. It plays no part in the rate.
• D. Temperature: affects the rate by increasing kinetic energy and effective collisions.

4. Answer The factor that does NOT affect the rate is the molecular weight of the products, which is option C.

5. Exam tip Rate factors concern the reactants and conditions (concentration, temperature, catalyst, surface area, pressure). If an option talks about the products or their properties, it is usually the distractor. Remember "CTCS": Concentration, Temperature, Catalyst, Surface area.