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Here is a video about partial pressures (15min): Partial Pressure Pressure, by Khan Academy, on YouTube

Here is another video about partial pressures (12min): Partial Pressure and Vapor Pressure, by Crash Course Chemistry, on YouTube

Partial Pressures

What if we have a mixture of different gases? We might want to know how much of each there is. We can define the mole fraction of a particular gas A as the number of moles of A divided by the total number of moles of gas:
x_A = n_A/n_total
Then we can define the partial pressure of A as
p_A = x_AP
This works for real or ideal gases. Partial pressures are often used to describe concentrations of gases. If the gas is ideal, then the partial pressure is the same pressure that the gas would make if all the other components of the mixture weren't there, because
p_A = n_ART/V
In a real gas, this might not be true because the different gases might interact a little bit differently.

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