1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Number of atoms reacting with a gas

  1. Mar 26, 2009 #1
    1. The problem statement, all variables and given/known data
    4Al + 3O2 = 2Al2O3
    What number of O-atoms will react if 45dm3 of the gas reacts with an excess of Al?
    The answer is apparently: 4 atoms

    2. Relevant equations

    3. The attempt at a solution
    Using the formula n=V/Vn (or the law stating that any gas occupies 22.4dm3 at STP), I found that the number of moles was (225/112) or 2.01. Then I used the formula: n=n*Na (number of moles times Avagadro's Constant) giving me 1.24*1024 atoms. Where did I go wrong please?
  2. jcsd
  3. Mar 26, 2009 #2


    User Avatar

    Staff: Mentor

    The answer is not 4 atoms.

    I have no idea what 225/112 means, even if the number of moles seems to correct.

    You have 45 L of the gas, there is 22.4 L per mole - how many moles of the gas?

    You have correctly converted number of moles of gas to number of molecules, however, you forgot that there is more than one atom per molecule.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook