At 4.00 l, an expandable vessel contains 0.864 mol of oxygen gas. how many liters of oxygen gas must be added at constant temperature and pressure if you need a total of 1.48mol of oxygen gas in the vessel?
express the volume to three significant figures, and include the appropriate units.

We first consider the ideal gas equation,

PV = nRT

It is stated that the pressure and temperature are constant; moreover, R is already a constant. So, we get:
V = constant * n
This is the equation of direct proportion. Therefore, we get:

V/n = constant

V₁/n₁ = V₂/n₂

Substitute the values and solve for V₂

V₂ = (4 * 1.48) / 0.864 
V₂ = 6.85

6.85 Liters of gas must be present at the end, so we need to add:
6.85 - 4 = 2.85 liters