A balloon filled with helium occupies 20.0 l at 1.50 atm and 25.0◦c. How many moles of helium will there be in the balloon at stp?

There will be 1.23 moles of helium in the balloon at STP

Explanation:

1) Initial conditions of the helium gas:

V = 20.0 liter p = 1.50 atm T = 25.0 °C = 25.0 + 273.15 K = 298.15 K

2) Ideal gas equation:

pV = n RT p, V, and T are given above R is the Universal constant = 0.0821 atm-liter / (K - mol) n is the unknown number of moles

3) Solve for n:

n = pV / (RT) = n = 1.50 atm * 20.0 liter / (0.0821 atm-liter / k - mol * 298.15K) n = 1.23 mol

4) At STP:

STP stands for standard pressure and temperature. The amount (number of moles) of the gas will not change because the change of pressure and temperature, so the number of moles reamain the same: 1.23 mol.