What does the term "mass transfer" refer to in chemical processes?

The term "mass transfer" in chemical processes specifically refers to the movement of mass from one location to another. This concept is crucial in various chemical engineering operations, such as distillation, absorption, and extraction, where substances are moved between phases (for example, from liquid to vapor) or from one part of a system to another. Mass transfer occurs due to concentration gradients and is driven by differences in chemical potential, temperature, or pressure. Understanding mass transfer is essential for optimizing reactions, separations, and overall process efficiency in both industrial and laboratory settings.