J.R. S. answered • 02/20/19

Ph.D. University Professor with 10+ years Tutoring Experience

PV = nRT (Ideal Gas Law)

P = pressure = ?

V = volume in liters = 2.5 L

n = moles of gas = 5.1 g He x 1 mole/4 g = 1.275 moles

R = gas constant = 0.0831 L-atm/K-mole

T = temperature in K = 23 + 273 = 296K

Solving for P:

P = nRT/V = (1.275 mol)(0.0821 L-atm/K-mol)(296)/2.5

P = 12.39 atm

Since they ask for the answer in units of torr, we convert as follows:

12.39 atm x 760 torr/1 atm = 9419 torr = 9400 torr (to 2 significant figures)