Mass transfer is the process by which substances move from one location to another, often driven by concentration differences. This can occur in various forms, such as diffusion, where particles spread from areas of high concentration to low concentration, or convection, where the movement of fluids carries substances along with it. In many industrial applications, such as in chemical engineering and environmental science, understanding mass transfer is crucial for designing efficient systems. For example, in distillation, absorption, and extraction, effective mass transfer ensures that desired components are separated or concentrated effectively.