Particle size, temperature, concentration difference and diffusion distance affect the rate of diffusion. The particle size highly influences the rate of diffusion. Since the heat of the environment is the energy source for diffusion, a smaller particle at a given temperature moves faster than a larger particle. The rate of diffusion shares an inversely proportional relationship with the particle size.
Temperature and the rate of diffusion have a directly proportional relationship with one another. The rate of diffusion increases as the temperature increases. At higher temperatures, particles move faster because more energy is available to diffuse them.
The rate of diffusion increases as the concentration difference increases. A substance diffusing between two areas exhibits a concentration difference as the particles diffuse from one side of the wall to the other side. For example, if a semipermeable bag of plain water is placed in salt water, the rate of diffusion increases because the salt water has a higher concentration of particles than the plain water.
The rate of diffusion is directly proportional to a particle's distance. It takes longer for a particle to diffuse when it is further away than it does for a particle that is closer to the point of diffusion.