Question

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?

Answer 1

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

Step-by-step 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.