Question

One classical test for diffusion control is to observe whether the rate of reaction is affected by stirring or agitation; if so then the reaction is almost certainly diffusion controlled under those conditions. How does stirring affect the rate of reaction in this scenario?

Answer 1

Stirring affects a diffusion-controlled chemical reaction by increasing molecule movement and the chances of reactant collisions, leading to a faster reaction rate.

Step-by-step explanation:

Stirring or agitation affects the rate of a chemical reaction that is diffusion-controlled by enhancing the movement of molecules, thereby increasing the chance of collisions between reactants. In diffusion-controlled reactions, reactants need to diffuse together before they can react. When a reaction is mixed through stirring, it ensures that more reactant molecules are brought into close proximity, speeding up the diffusion process. This results in a greater number of effective collisions per unit of time and thereby an increased reaction rate. Without stirring, reactants may take longer to diffuse through the solvent, which can slow down the reaction rate.

For example, if you place a drop of food coloring in a glass of water without stirring, the color will spread slowly. This represents free diffusion, where the movement of molecules is due to their natural, random motion. Stirring evenly distributes the coloring more quickly than if the system is left undisturbed, showcasing the diffusion control in this scenario.