Question

A cylinder contains 91.3 g of oxygen gas. If the volume of the cylinder is 8.58 grams, what is the pressure of the gas in atmospheres if gas temperature is 21 ^oC? Calculate the pressure using the ideal gas equation and the van der Waals equation.

Answer 1

1. Ideal gas equation

PV = nRT

P= Pressure

V = Volume = 8.58 L = 0.00858m3

T = 21 degree C = 294 K

n = moles = mass / molecular wt = 91.3 / 32 = 2.85

P = nRT / V = 2.85 X 8.314 X 294 / 0.00858 = 811923.14 Pascal

Now we will use Van Der waals equation

(P + n²a / V²) (V-nb) = nRT

a = measure of attraction between particles = 0.1378 ( for oxygen)

b = excluded volume = 0.00003183 ( for oxygen)

So

(P + (2.85)² (0.1378) / (0.00858)²) (0.00858)- 2.85 X 0.00003183) = 2.85 X 8.314 X 294

On solving the whole equation

Pressure = 803054.2 Pascal