Partial pressure and Kp calculations

The partial pressure of a gas is the pressure that the gas would have if it was in the container all by itself. It can be calculated if you know the total pressure and the mole fraction of the gas concerned.

Partial pressure of gas A = mole fraction of A    x     total pressure 

(using symbols,     p_A   =    X_A     x     P_tot   )

 The mole fraction is simply the number of moles of the gas you are interested in divided by the total number of moles of gas in the container.

(again in symbols,    X_A    =    n_A   /  (n_A +  n_B  +  n_C  +  n_D  etc)

This video shows how to work out the partial pressures of various gases in a container.