For the combustion reaction 4"NH"_3(g) + 5"O"_2(g) -> 4"NO"(g) + 6"H"_2"O"(g)4NH3(g)+5O2(g)4NO(g)+6H2O(g), how many liters of "O"_2(g)O2(g) would react with "500 L"500 L of "NH"_3NH3 at STP?

1 Answer
Apr 30, 2017

"625 L O"_2625 L O2


This is a limiting reactant problem using gases (assumed ideal).

Given "500 L"500 L of "NH"_3NH3, since we are at STP (presumably, "1 atm"1 atm and 0^@ "C"0C), we can determine the molar volume of "NH"_3NH3 by assuming it is an ideal gas.

PV = nRTPV=nRT

V/n = (RT)/PVn=RTP

= (("0.082057 L"cdotcancel"atm""/mol"cdotcancel"K")(273.15 cancel"K"))/(cancel"1 atm")

= "22.41 L/mol"

Therefore, we have

500 cancel("L NH"_3) xx "1 mol"/(22.41 cancel("L NH"_3(g)))

= "22.31 mols NH"_3

From the reaction given, there needs to be "5 mols O"_2(g) for every "4 mols NH"_3(g). Therefore:

22.31 cancel("mols NH"_3) xx ("5 mols O"_2)/(4 cancel("mols NH"_3))

= "27.88 mols O"_2

Since we are also assuming "O"_2(g) is an ideal gas, we utilize the same molar volume to get:

27.88 cancel("mols O"_2(g)) xx "22.41 L"/cancel("mol O"_2(g))

= color(blue)("625 L O"_2(g))

You could also have gone straight from the volume and used the mol ratio by ASSUMING that both "O"_2(g) and "NH"_3(g) are ideal gases:

"500 L" cancel("NH"_3) xx (5 cancel"mols" "O"_2)/(4 cancel"mols" cancel("NH"_3))

= color(blue)("625 L O"_2(g))