The surface area of a reactant affects the rate of a chemical reaction by influencing the number of collisions between reactant particles. The relationship between the surface area and the rate of a chemical reaction can be explained using the collision theory, which states that for a reaction to occur, reactant particles must collide with each other with sufficient energy and proper orientation.When the surface area of a reactant is increased, more particles are exposed and available for collisions with other reactant particles. This leads to a higher probability of successful collisions, which in turn increases the rate of the chemical reaction. Conversely, when the surface area of a reactant is decreased, fewer particles are exposed, resulting in fewer collisions and a slower reaction rate.In summary, the relationship between the surface area of a reactant and the rate of a chemical reaction is directly proportional: as the surface area increases, the rate of the reaction also increases, and as the surface area decreases, the rate of the reaction decreases. This relationship is particularly important in heterogeneous reactions, where reactants are in different phases e.g., solid and gas , and the reaction occurs at the interface between the phases.