Diffusion
Diffusion is the net movement of particles from a region of higher concentration
to the region of lower concentration following concentration gradient as the
result of random, spontaneous movement. Diffusion is a passive / spontaneous
process that does not require energy.
Rate of diffusion – speed at which diffusion takes place, i.e. number of particles
travelling per period of time.
Factors affecting the rate of diffusion:
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Concentration gradient
Diffusion distance
Surface Area
Temperature
Concentration Gradient
Solution with high concentration: Concentrated solution
Solution with low concentration: Dilute solution
Concentration Gradient takes place when two solutions have different
concentration. The bigger the difference in concentrations the steeper
the concentration difference, and faster the rate of diffusion.
Diffusion Distance
Distance needed to be traveled by moving particles.
Shorter the distance, faster the rate of diffusion.
Example: Projections on intestinal lining have very thin epithelial layer for
increased rate of diffusion.
Surface Area
Diffusion takes place at surface area, thus larger the surface area, faster the rate
of diffusion.
When one large cube is broken down into smaller cubes diffusion will take place at each side of every
small cube, hence diffusion rate would increase.
Analogy:
Large sugar cube would take more time to be dissolved in hot tea, whereas if you break the
same large sugar cube into small pieces it will be dissolved quickly.
Temperature
Diffusion is a random movement of particles. According to Kinetic Theory, particles move because their
kinetic energy is higher than potential energy. Increase in temperature means increase in heat energy,
which is converted into kinetic energy of particles. As kinetic energy of particles increases, they move
faster, causing faster diffusion rate.
Higher the temperature, faster the rate of diffusion.
Analogy:
Sugar dissolves faster in hot tea then in iced tea.