Question

What volume will 2.04 grams of He has occupy at 100°C and 785 mm Hg or pressure?

Answer 1

He is a gas and to find the volume, the gas law can be used

PV = nRT

P= Pressure of the gas (Pa)
V = Volume of the gas (m³)
n = Moles (mol)
R = Universal gas constant (8.314 J mol⁻¹ K⁻¹)
T = Temperature in Kelvin (K)

P= 785 mm Hg = 1.05 x 10⁵ Pa
n = mass / molar mass
   = 2.04 g / 4.00 g mol⁻¹
   = 0.51 mol
R = 8.314 J mol⁻¹ K⁻¹
T = 273 + 100 K = 373 K

By adding those values to the above equation volume can be calculated.

hence volume = nRT / P
                   V = 0.51 x 8.314 x 373 / 1.05 x 10⁵
                   V = 15.06 x 10⁻³ m³