The effect when molecules move from an area of high concentration to an area of low concentration is known as diffusion. This process occurs spontaneously and continues until there is an equal distribution of molecules throughout the medium. Diffusion is essential in various biological and physical processes, including gas exchange in the lungs, nutrient absorption in cells, and the spreading of fragrances in the air. It is a fundamental principle in chemistry and biology that illustrates how substances interact in different environments.