The rate of a chemical reaction is NOT affected by one of these factors

Step 1: Analyze the question We are asked which factor does NOT affect the rate of a chemical reaction.

Step 2: Recall the concept Reaction rate depends on factors that change how often and how energetically particles collide:

• Concentration: more particles in a given volume means more frequent collisions, so a faster rate.
• Surface area: a finely divided solid exposes more particles, so a faster rate (e.g., powdered CaCO₃ reacts faster with HCl than lumps).
• Temperature: higher temperature gives particles more kinetic energy, so more of them exceed the activation energy.
• Presence of light: some reactions are light-sensitive (photochemical), such as photosynthesis, the decomposition of silver chloride or silver bromide, and the reaction of H₂ with Cl₂.
• Catalysts and pressure (for gases) also affect the rate.

Step 3: Evaluate each option

• A. Colour: the colour of a reactant is just a physical appearance and does not change the collision frequency or the energy needed. It is not a rate-determining factor.
• B. Concentration: affects the rate.
• C. Presence of light: affects the rate for photochemical reactions.
• D. Surface area: affects the rate.
• E. Temperature: affects the rate.

Step 4: Answer The factor that does not affect the rate of a reaction is colour, which is option A.

Exam tip: In "NOT affected" questions, first cross out the factors you know from collision theory (concentration, surface area, temperature, catalyst, pressure, light). The option left over is usually the answer. Colour, on its own, is never one of them.