The rate of diffusion of gases

 

Gases diffuse because the particles collide with other particles, and bounce off in all directions . if you do not know what exactly diffusion means click here first

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Note that gases do not all diffuse at the same rate.

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The speed with which the gases diffuse depends on these two factors:

 

 

1 The mass of the particles

 

The particles in hydrogen chloride gas are twice as heavy as those in ammonia gas.

 

 

Cotton wool soaked in ammonia solution is put into one end of a long tube

(at A below). It gives off ammonia gas. 

 

At the same time, cotton wool soaked in hydrochloric acid is put into the other end of the tube (at B). It gives off hydrogen chloride gas. 

 

 

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The gases diffuse along the tube. White smoke forms where they meet: The white smoke forms closer to B. So the ammonia particles have travelled further than the hydrogen chloride particles – which means they have travelled faster.

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The lower the mass of its particles, the faster a gas will diffuse.

 

When particles collide and bounce away, the lighter particles will bounce further. The particles in the two gases above are molecules.

 

The mass of a molecule is called its relative molecular mass.

 

So The lower its relative molecular mass, the faster a gas will diffuse.

 

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2 The temperature

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When a gas is heated its particles take in heat energy, and move faster. They collide with more energy, and bounce further away. So the gas diffuses faster. The higher the temperature, the faster a gas will diffuse.