Investigation 10: Kinetics and Rate of Reaction

The reaction is CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H_2O(l) + CO₂(g). Because CO₂ bubbles away, the flask loses mass over time, and that mass loss tracks how much reaction has happened. Rate depends on how often particles collide with enough energy to react. Grinding the marble into powder exposes far more surface area, so more acid particles touch solid calcium carbonate at once and the fizzing is faster. Raising acid concentration packs more HCl particles into the same volume, raising collision frequency. Raising temperature gives particles more kinetic energy, so a larger fraction of collisions clear the activation energy barrier. All three speed up the reaction without changing how much product the full reaction can eventually make.

To read rate from data, you plot mass (or mass lost) against time. The curve is steepest at the very start, when reactant concentration is highest, and that initial slope is the initial rate. As reactant is used up, the curve flattens into a plateau once the limiting reactant is gone and bubbling stops. A common trap is assuming a steeper early slope means more total product. It doesn't: rate describes speed, yield describes amount, and they're controlled by different things. A catalyst or finer powder gets you to the same plateau height faster, not higher.

This investigation sits alongside the broader kinetics unit on collision theory and rate laws, and it reinforces science practices used across the 16 labs: translating a graph's slope into a physical rate, distinguishing a measured quantity (mass) from a derived one (rate), and reasoning about limiting reactant behavior when a curve bends toward its plateau.