By Diane Evans Updated Aug 30, 2022
The rate of a chemical reaction is the speed at which reactants transform into products. Collision theory explains that reactions require sufficient energy for reactant particles to collide, break bonds, and form new compounds. The mass of reactant particles influences the available surface area for collisions, thereby affecting the reaction rate.
Several factors—such as mass, concentration, temperature, and particle size—shape how quickly a reaction proceeds. Smaller, lighter particles present more surface area for collisions, accelerating the rate. In contrast, large, complex molecules with remote reactive sites may react slowly, even when collisions are frequent.
Increasing the concentration of reactants typically speeds up a reaction because more particles are available to collide over time. However, for reactions involving large biomolecules like proteins, higher concentrations may not always translate to faster rates, as the reactive sites can be buried within the molecular structure.
Heat supplies kinetic energy, raising particle velocity and collision frequency. Small, lightweight particles require less heat to reach the energy threshold, whereas excessive heat can denature large proteins, disrupting their structure and reducing reactivity.
When a solid reactant is finely ground into a powder, its surface area increases, exposing more reactive sites and enhancing the reaction rate. Graphically, reaction progress often starts rapidly when concentrations are high and gradually slows as reactants are consumed, eventually plateauing when the reaction reaches completion.
