diffusion

• diffusion - random net movement of molecules down a concentration gradient, from area of high concentration to a low area, across a semi-permeable membrane
• Dynamic equilibrium - when two processes take place at the same rate so there is no further change in concentration of the substance
• semi - permeable membrane - membrane that allows small molecules such as water, CO2 and O2 pass through it, but will not allow large molecules to pass through it
• surface area

  larger surface area, faster rate of diffusion. Due to:

  • more surface area for particles to diffuse across
  • more particles can diffuse at same time
  • more contact between substance and surface the substance is diffusing across
• concentration gradient

  • greater the concentration gradient, faster rate of diffusion
  • all molecules move down gradient, gradient evens out until the dynamic equilibrium is reached
• diffusion distance

  • smaller the diffusion pathway, faster the rate of diffusion
  • particles can travel shorter distances quicker than longer distances
• temperature

  higher the temperature, the faster the rate of diffusion. Due to:

  • higher the temperature, more kinetic energy to particles
  • particles will move faster
  • more collisions (in given time)
• size and shape of molecule

  lighter the molecular weight of a molecule, the faster the rate of diffusion. Due to:

  • smaller lighter molecules move faster compared to larger heavier molecules
  • more kinetic energy is needed to move a larger molecule at the same speed as a small molecule
  • more streamlined shape (long thin) of a molecule, the faster rate of diffusion than less streamlined (fat bulky) molecule of a similar molecular mass
• absolute zero - the lowest possible temperature, which is 0 kelvin and -273c on a Celsius scale
• kinetic model of matter

  all matter is made up of very small particles (atoms, molecules or ions) which are in constant motion
• rate of diffusion = surface area x concentration gradient % diffusion distance
• The particle model

  Particles within solids are touching each other and arranged in fixed positions. Particles in liquids are closed together, rolling over each other and arranged randomly.

  Particles in gases are far apart and arranged randomly.
• Kinetic theory

  At absolute zero (0 kelvin or -273 degrees Celsius), there is no movement of particles. Any temperature above this cause particles in solids, liquids and gases to move. In a solid, particles can vibrate in all directions but cannot move out of their fixed positions. In a liquid, the particles move randomly and can slide past each other, but they do not move far.
• Kinetic theory pt2

  In a gas, the particles move around quickly and can travel large distances in all directions. The molecules in a gas are constantly hitting each other and the walls of their container, causing them to change direction. In all states of matter, if temperature is increased, the particles will gain more kinetic energy and vibrate or move more quickly.