# Doesn't adding an inert gas at constant volume increase the partial pressures?

When you add an inert gas to a container of constant volume full of gases, you are basically shoving the inert gas into the container and increasing the pressure inside the container, so the partial pressures of all the gases increase don't they?

• Ohhhh, I thought because the total pressure increases the partial pressures would increase too. But, doesnt the argon put extra pressure on the N2 and O2? Mar 30 at 7:41
• Ohhhhk thank you so much! Mar 30 at 7:51

Why should they ( supposing ideal gas behaviour ) ?

If a volume, containing $$\pu{4 mol}$$ $$\ce{N2}$$ and $$\pu{1 mol}$$ $$\ce{O2}$$ has pressure $$\pu{5 atm}$$, partial pressures are:

$$\ce{N2} : \pu{4 atm}$$
$$\ce{O2} : \pu{1 atm}$$

If you add $$\pu{5 mol}$$ $$\ce{Ar}$$, the total pressure raises to $$\pu{10 atm}$$, with partial pressures :

$$\ce{Ar} : \pu{5 atm}$$
$$\ce{N2} : \pu{4 atm}$$
$$\ce{O2} : \pu{1 atm}$$

Note that pressure is macroscopic quantity. Partial pressure of any gas is determined by frequency of collisions with a wall unit area, and by passed impulse by 1 molecule.