Question

What is the formula of partial pressure?

Answer 1

For an ideal gas, the partial pressure relationship is called Henry's Law. It's just the total pressure `P_"tot"` multiplied by the mole fraction `x_j` of the mixture that is occupied by component `j`.

`P_j = x_jP_"tot"`

You're really just multiplying the total pressure by the percentage corresponding to one component. So if the total pressure was `1` atm, then if the partial pressure of component `j` is `0.8` atm, its mole fraction is `(0.8 cancel(atm))/ (1 cancel(atm)) = 0.8`.