Modern vacuum pumps can evacuate a vessel down to a pressure of 4.0 × 1 0 ^ - 1 5 atm. at room temperature (300 K). Taking R = 8.3 JK -1 mole -1 , 1 atm = 10 5 Pa and N _ Avogadro = 6 × 1 0 ^ 2 3 mole ^ - 1 , the mean

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Quantrex Academy · Accepted Answer

Correct answer: B. 0 . 2mm

Let the inter molecular distance be D
Then in a volume of

\dfrac{4}{3} \pi{D}^{3}

there is only one molecule.

\dfrac{4}{3} \pi{D}^{3} P = ( \dfrac{1}{{N}_{A}} )RT

D = {( \dfrac{3RT}{4\pi{N}_{A} P} )}^{\dfrac{1}{3}}

Substituting

P = 4 \times {10}^{- 10} Pa, R = 8.3, {N}_{A} = 6 \times {10}^{23} , T = 300K

D = 0.2mm

Modern vacuum pumps can evacuate a vessel down to a pressure of 4.0...

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