Summary
Highlights
This video will explain how the surface area of solid reactants affects the rate of chemical reactions. Recall that chemical reactions occur when particles collide with sufficient energy, and the rate is determined by the frequency of successful collisions. We will now focus on how surface area impacts this frequency.
Particles in solution or gas can only react with particles on the surface of a solid reactant. A solid block has many internal particles that are unavailable for reaction. By breaking the solid into smaller pieces, the surface area increases, making more particles available for collision. This leads to a greater number of collisions per second and thus an increased reaction rate.
Smaller blocks of solid reactants have a greater surface area to volume ratio compared to larger blocks. This means more particles are exposed on the surface, increasing the frequency of successful collisions and accelerating the reaction rate.
A common experiment to investigate the effect of surface area uses marble chips (calcium carbonate) reacting with hydrochloric acid to produce carbon dioxide gas. The volume of produced CO2 can be measured using a measuring cylinder or a more accurate gas syringe to determine the reaction rate. Changing the size of the marble chips allows for observation of surface area effects.
Another method to track the reaction rate is by measuring the loss of mass as carbon dioxide gas escapes. The reaction flask is placed on a balance, and the decreasing mass indicates the rate of CO2 production. A cotton-wool plug prevents acid from splashing out, which would lead to inaccurate mass readings, while still allowing the gas to escape.