posted by bill .
when ammonium nitrate decomposes, nitrogen, hydrogen, and oxygen gas are generated per the reaction 2NH4NO3(s)=2N2(g)+4H2+3O2(g). when 23 g NH4NO3 decomposes what total volume of gas at 1 atm and 298 do you get?
Convert 23 g NH4NO3 to mols. mols = grams/molar mass.
For every 2 mols of NH4NO3 that decomposes you obtain 2 mols N2 + 4 mols H2 + 3 mols oxygen. So you obtain 9 mols gas per 2 mols NH4NO3 or 9/2 mols gas/mol NH4NO3. After you determine total mols gas, then use PV = nRT to convert mol at STP to mols at 1 atm and 298. Post your work if you get stuck.
Looks ok to me.