Gas/pressure Problem

[TexasFluoride]

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A 40.0-L automobile gasoline tank is half full of fuel. At standard pressure, if the temperature in the tank is 7 °C, how much vapor is in the tank? (R = 0.08206 L·atm/mol·K)

The answer is 0.87 mol.


I understand how to work the problem but I don’t understand why we consider volume to be 20L in the PV=Nrt equation when we are solving for N(moles). Yes I understand that it is a half tank of gas. But the gas itself is still occupying a volume of 40L.

Anyone can further explain why we consider volume to be 20L?? thanks

 

[jazun2390]

Gasoline is a liquid, and it's occupying 20.0L of the 40L tank. The vapor would occupy the space above the liquid, the remaining 20L 🙂