hey i'm going through an exam paper and i'm having a difficult time working them out. any help will be greatly appreciated. thanks! the first question is for the size of an atom.. The second virial coefficient, B, at high temperatures equals half the excluded volume due to the repulsive part of the intermolecular forces. Use B=11.9 cm3 mol-1 for Argon to estimate the range (in nm) of the repulsive part of the interatomic forces between argon atoms. (Hint: Imagine the Argon gas to be like a collection of billiard balls in 3D with the excluded volume being the volume occupied by the balls themselves.) :uhh: i have gone through that question many times and havent been able to find an equation for it.. all i could think of was avragardo's no. NA/B.. what else can i do..? my second question is to.. determine the ratio of the mean speeds of oxygen and nitrogen molecules in air at 28°C and at a pressure of 1 bar do i just find the mean speed of each molecule and find the ratio? using the question (8RT/(pi*M)^0.5 = (3kT/m)^0.5 where M=m*NA=mass of one mole. would M be in g or Kg..? (i'm too use to chemistry, using grams) and my final question i am having trouble with uses a big formulae i think.. it asks me to find the pressure (in Pa) at which the mean free path of argon at 23°C becomes comparable to the diameter of a 1L spherical vessel that contains it (cross section of argon = 0.36nm^2 i'm using the equation where λ = c/((N/V)*σ*crel = kT/(sqrt2)σp and rearanging it in terms of P to find the pressure so much hassle sorry for writing so much but i find these questions really tough. am i going about these questions the wrong way.. or are these tougher than usual pls help mee...=( thanks!