What is the volume after...

Question

A sample containing 5.60 g O2 gas has a volume of 29.0 L . Pressure and temperature remain constant.

What is the volume after 7.50 g He is added to the O2 gas already in the container?

Answer 1

Since pressure and temperature remain constant, but the number of moles of gas (n) are changing, we are essentially dealing with Avogadro's Law, which states that equal volumes of any gas, at the same temperature and pressure, have the same number of molecules. An extension of this tells us that different number of molecules (moles) will occupy different volumes.

We can look at this as V1/n1 = V2/n2

V1 = 29.0 L

n1 = 5.60 g O2 x 1 mole/32 g = 0.175 moles O2

V2 = ?

n2 = moles O2 + moles He = 0.175 moles = 0.175 + 7.50g/4 mol/g = 0.175 mol + 1.875 mol = 2.05 moles

29.0 L/0.175 moles = V2/2.05 moles

V2 = (29.0 L)(2.05 moles)/0.175 moles = 340 L