A 20.0L tank contains 0.225 kg of helium at 18 degrees celcius. The molar mass of helium is 4.00 g/mol.
1. How many moles of helium are in the tank?
2. What is the pressure in the tank in Pascals and in atmospheres?
(a)Given : Volume of tank = 20.0 L
Mass of helium gas = 0.225 Kg = 225
g (Since 1 Kg = 1000 g)
And temperature of gas = 18 oC
1. The moles of helium in the can is given by,
=> Moles of He =
= 56.25 mol.
(b) According to ideal gas law,
=> PV = nRT
where P = pressure in atm
V = volume in L = 20.0 L
n = moles = 56.25 mol.
R = gas constant = 0.0821 atm.L/K.mol
T = temperature in K = T in °C + 273 = 273 + 18 = 291 K
Hence substituting the values we get,
=> P X 20.0 = 56.25 X 0.0821 X 291
=> P = Pressure in tank = 67.2 atm.
Since 1 atm = 101325 Pa
Hence pressure in tank in Pa = 67.2 X 101325 = 6.81 X 106 Pa approx.