Which of the following factors will affect the rate of the reaction represented by the following equation?…

Analyze the question: We need the factors that affect the rate of the reaction between dilute hydrochloric acid (aqueous) and calcium carbonate (solid), which produces CO₂ gas.

Concept: Reaction rate depends on how often and how effectively particles collide. The main factors are:

• Concentration of reactants in solution (higher concentration means more frequent collisions)
• Temperature (higher temperature means more energetic particles and more effective collisions)
• Nature of reactants (different substances react at different intrinsic rates)
• Surface area of solids (not listed here)
• Catalyst (not listed here)
• Pressure, which matters only when the reactants are gases

Step-by-step evaluation:

I. Pressure: The reactants are an aqueous solution and a solid. The only gas, CO₂, is a product. Pressure changes affect the rate significantly only when gaseous reactants are involved, so pressure is not a significant factor here.

II. Concentration: Changing the concentration of HCl changes the rate. This is a factor.

III. Nature of reactants: The identity of the reactants (an acid and a metal carbonate) determines how fast the reaction proceeds. This is a factor.

IV. Temperature: Heating speeds up the reaction. This is a factor.

So the factors are II, III and IV only.

Answer: B

Tip: In rate-of-reaction questions, check the physical states first. Pressure matters only if gaseous reactants are present. A gas appearing only as a product (like CO₂ here) does not make pressure a factor. WAEC often uses this trap.