Question

A 30-cm-diameter cylinder of helium gas is 20 cm long and at 14 degrees C. The pressure gauge reads 120 psi.

Part A: How many helium atoms are in the cylinder?

N = ______ atoms

Part B: What is the mass of the helium?

m = ___value___ ___units___

Answer 1

Using this instead:

pV = NkT

Where, p = pressure (kPa), V = volume (L), N = number of atoms/molecules, k = Boltzmanns constant, T = temperature (in K).

For P, use (120 + 14.7) psi since you must use absolute pressure in this calculation.

p = (120+14.7) * 6894.75729 / 1000

p = 928.724 kPa

V = pi*(30/2)^2 * 20 / 1000

V = 14.14 L

T = 14 + 273.15

T = 287.15

pV = NkT

928.724 * 14.14 = N * 1.38065 * 10^-23 * 287.15

N = 3.31 * 10^24 to three significant figures.