Systems are often not in equilibrium; that is, the movement of materials into and out of the system is not equal. Diffusion is a movement in which the net direction of movement is from an area of high concentration to an area of low concentration. When equilibrium is reached, the concentration on both sides should be equal. However, it is important to know that even at equilibrium, the movement between the two sides still occurs, but the rate of movement is the same. Another important thing to keep in mind is that diffusion is a passive process so no energy is used.
diffusion of ink in water
Diffusion of water across a semipermeable membrane from the side with dilute sugar concentration to the side with concentrated sugar concentration (ie: from the side with higher water concentration to the side with lower water concentration. The diffusion of water is also called osmosis
When you spray perfume in one spot, the scent travels beyond that spot because the molecules in the perfume are diffusing from where they are more concentrated to where they are less concentrated. In another word, the molecules are spreading out.
Mr. Gao and Mr. Martin