Question

9. Suppose two gases in a container have a total pressure of 1.20 atm. What is the pressure of gas B if the partial pressure of gas A is 0.75 atm?

Answer 1

`P_B=0.45*atm`

Explanation:

Dalton's Law of partial pressure holds that in a gaseous mixture, the pressure exerted by a component is the same as the pressure it would exert if it ALONE occupied the container. The total pressure is the sum of the individual partial pressure.

i.e. `P_"Total"=P_1+P_2+P_3.........`

And here `P_"Total"=1.20*atm=P_A+P_B=0.75*atm+P_B`,

i.e. `P_B=1.20*atm-0.75*atm=??*atm.`

Note that we can use this law to access the number of moles of each gas, given that `P=(nRT)/V`,

i.e. `P_"Total"=(RT)/V{n_1+n_2+...........n_n}`, where `n_i` is the number of moles of gas `i`.

And we can show that:

`P_i/P_"Total"=n_i/n_"Total"`,

i.e. partial pressure is equivalent to mole fraction.