Diffusion and effusion

The diffusion refers to mixing two gases together. For example, the aroma of a meal when entering a room is a consequence of the mixture of two gases. That is its dissemination.

All diffusion always occurs:
  • From a higher concentration to a lower concentration point.
  • It is a gradual process since the molecule undergoes various modifications in diffusion with the other gaseous molecules.
  • The speed of said diffusion will depend on the lightness or heaviness of each gas. Thus, there are heavy gases whose diffusion is slower and others (lighter gases) whose diffusion is faster.

Graham’s broadcast law

If the pressure and temperature conditions are the same, the rate of diffusion of the gases is inversely proportional to the square roots of their molar masses.

  • It can serve you: Gas mixtures.


The effusion is the process by which a gas escapes outside a container through a small opening or crack in it. Thus the effusion rate is directly proportional to the speed of the molecules.

This means that, if a heavy gas molecule has an effusion, it will do so more slowly than a lighter gas molecule, in which case the effusion will be faster. A deflated balloon is an example of effusion.

Effusion examples


  • Depressing the button of a deodorant
  • Rotate a burner knob to turn it on or off
  • A helium container with a leak
  • A hot air balloon presenting a loss
  • Powered backpacks
  • Astronauts gas pipes
  • A deflating balloon
  • Flatulence
  • The separation of uranium 238 into uranium 235
  • A gas cylinder with a small leak through which it moves to another compartment or to the outside.

Examples of diffusion


  • When making coffee, the aroma is usually spread throughout the room.
  • The perfume of flowers indoors
  • A pleasant aroma or not that spreads throughout an entire room
  • When a person perfumes himself and enters a room and everyone can smell his perfume
  • Smoke to give off cars in circulation
  • Smoke from chimneys of homes or factories
  • The smell of decomposing food inside the fridge
  • The smell of a scented candle, incense, or match
  • Smoke from a cigarette in an airtight room
  • Aromatic essences
  • The smell of a rotten egg inside a container

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