Question

How many moles of helium are present in a balloon at STP if the volume is 3.5 L?

Answer 1

mole=stp par volume÷22.4
mole=3.5÷22.4
=0.15625

Answer 2

It appears that : 1 mole of a gas, at STP occupies 22.4 L. STP – standard temperature and pressure. STP - 0ºC, 101.3 kPa (1 atm, 760 mmHg)

GIVEN,

             volume of helium are present in a balloon at STP = 3.5L

moles of helium present in balloon = STP  per volume / 22.4 L

moles of helium present in balloon = 3.5 / 22.4

                                                          =0.15625 kPa