The highest rate of production of carbon (lV) oxide can be achieved using

Analyze the question: We want the fastest rate of CO₂ production from the reaction of HCl with CaCO₃:

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

Concept: Rate of reaction depends on:

1. Concentration of the reactant. Higher concentration means more frequent collisions, so a faster rate.
2. Surface area of the solid. Powder has a much larger surface area than lumps, so it reacts faster.

(The options are written as "mol dm⁻³" HCl, so the number is the concentration.)

Solution:

• A: 0.05 mol dm⁻³, powdered. Moderate concentration, large surface area.
• B: 0.05 mol dm⁻³, lump. Moderate concentration, small surface area, so slower than A.
• C: 0.10 mol dm⁻³, powdered. Highest concentration, large surface area.
• D: 0.025 mol dm⁻³, powdered. Lowest concentration, so slower than A.

Option C combines the highest acid concentration (0.10) with the largest surface area (powder), so it gives the highest rate.

Answer: C

Exam tip: For "highest rate" questions, look for the option with the highest concentration, highest temperature, and finest particle size (powder). If one option has all of these, that is your answer.