Factors that affect the rate of diffusion

What factors affect the rate of diffusion seen in the 3 practicals.

The Surface Area: As it increases, the rate of diffusion increases.

• Practical 3 with the agar cubes of different SA.

The Concentration gradient: As it increases, the rate of diffusion increases.

• Practical 2 with the different concentrations of HCl

The temperature: As it increases, the rate of diffusion increases.

• Practical 1 with the different temperatures of water.

How do smaller/larger molecules affect the rate of diffusion?

Smaller molecules move at a quicker rate from a region of high concentration to a region of low conc, down a concentration gradient.

• Can pass through the membrane

Larger molecules move at a slower rate from a region of high conc to a regions of low conc, down a concentration gradient.

• Cannot pass through the membrane

When diffusing through a membrane, some molecules cannot go through because of their shape or size.

• This is why plasma membranes are called semi-permeable.

How can the size of the diffusion pathway affect the rate of diffusion?

The shorter the diffusion pathway the greater the rate of diffusion.

The longer the diffusion pathway the smaller the rate of diffusion.

How can the energy of molecules affect the rate of diffusion?

The higher the energy in particles, the more kinetic energy there is so the movement will increases. Increasing the rate of diffusion.

How can the barriers and membrane affect the rate of diffusion?

The less barriers or membranes present the quicker the particles will be able to move through them increasing the rate of diffusion.

What is a dynamic equailibrium?

For example, after adding food colouring to water the molcules will move from a hign concentration to an area of low concentration down a concentartion gradient.

• This will create a dynamic equilibrium as the molecules are evenly distributed.