Question

How many moles of He (g) are in a 5 L storage tank filled with He at 10.5 atm pressure and 30°C?

Answer 1

Approx. `2*mol`

Explanation:

`n=(PV)/(RT)=(10.5*atmxx5*L)/(0.0821*L*atm*K^-1*mol^-1xx303*K)`

`=??mol`

The only difficulty with these sorts of problems is selecting the right gas constant `R`.

Chemists tend to use `R=0.0821*L*atm*K^-1*mol^-1`, because the units of `"litres"` and `"atmospheres"` are convenient. Note that you really don't have to remember them because they should be provided to you in an exam.