Final answer:
The rate of reaction between calcium carbonate and hydrochloric acid changes because as the reaction progresses, the concentrations of reactants decrease, leading to fewer effective collisions and a slower rate.
Step-by-step explanation:
In terms of particles, the rate of reaction between calcium carbonate (CaCO3) and hydrochloric acid (HCl) fluctuates during the reaction process due to changes in reactant concentrations. At the beginning of the reaction, there are plenty of CaCO3 and HCl particles available to collide with each other, resulting in a faster initial rate. As the reaction progresses, the concentration of these reactants decreases because CaCO3 is being consumed to form calcium chloride (CaCl2), water (H2O), and carbon dioxide (CO2) gas, which results in fewer effective collisions per unit of time and thus a slower reaction rate.
The reaction can be represented by the equation: CaCO3(s) + 2HCl(aq) -> CaCl2(aq) + CO2(g) + H2O(l). Over time, the particles of CaCO3 become fewer, and also the relative motion among particles may decrease as the acid is neutralized, further contributing to the decreasing reaction rate.