How many gas molecules

  • Thread starter noname1
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  • #1
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An excellent laboratory vacuum has a pressure of 4.00x10^-18 atm, or 4.04x10^-13 Pa. How many gas molecules are there per cubic centimeter in such a vacuum at 297 K?

n/v = p/rt


n/v = 4.04x10^-13 / (8.31x297) = 1.66x10^-16 mol/m³

1.66x10^-16 mol/m³ * (1/100cm)³ = 1.66x10^-22 mol/cm³

but something is wrong, please verify and she what i am doing wrong
 

Answers and Replies

  • #2
rock.freak667
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1 mole contains how many molecules?
 
  • #4
rock.freak667
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6.22x10^23
And you have 1.66x10-22 moles, so how many molecules do you have?


Actually now that I see it, you are finding per cm3.

R has the units J/mol.K

J = 1 Pa m3, so you'll need to change your units for R for it to work out properly.
 
  • #5
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ok i see it now i forgot to multiply by (6.022x10^23/mol)

i only got 1 more try at answering this question :(

(1.66x10^-16 mol/m³) * (m/100cm)³ * (6.022x10^23/mol) = 99.97 molecules/cm³

am i correct now?
 

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