Solid calcium carbonate reacts with 1.0 M hydrochloric acid according to the equation
CaCO₃(s) + 2 HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l)
Two samples containing equal masses of CaCO₃ but differing in particle size were reacted separately under identical conditions (same temperature, same initial acid concentration, same total volume).
The cumulative mass of CO₂ released was recorded every 10 s for 60 s. The data are shown below.
Time (s) | Mass of CO₂ released (g) — Sample A (large chips) | Mass of CO₂ released (g) — Sample B (finely powdered)
0 | 0.000 | 0.000
10 | 0.021 | 0.094
20 | 0.038 | 0.165
30 | 0.051 | 0.215
40 | 0.059 | 0.244
50 | 0.063 | 0.260
60 | 0.065 | 0.267
Answer the following questions about the experiment.
(a) Using the data, determine during which 10 s interval each sample exhibits its greatest average rate of CO₂ formation. Show how you arrived at your decision.
(b) Compare quantitatively the maximum average rates for Sample A and Sample B. State the factor by which the rate changes when the large chips are replaced by the powder.
(c) Explain, at the particulate level, why the powdered sample reacts faster than the large chips, even though both samples contain the same mass of CaCO₃.
(d) Predict how vigorous stirring of Sample A during the first 30 s would affect its rate of CO₂ evolution. Justify your prediction by referring to molecular collisions.