Molecular Speeds: a Cubic Box with Sides of 20

Multiple Choice

Molecular speeds: A cubic box with sides of 20.0 cm contains 2.00 × 10²³ molecules of helium with a root-mean-square speed (thermal speed) of 200 m/s. The mass of a helium molecule is 3.40 × 10^-27 kg. What is the average pressure exerted by the molecules on the walls of the container? The Boltzmann constant is 1.38 × 10^-23 J/K and the ideal gas constant is R = 8.314 J/mol ∙ K = 0.0821 L ∙ atm/mol ∙ K.

A) 3.39 kPa
B) 1.13 kPa
C) 570 Pa
D) 2.26 kPa
E) 9.10 Pa