Your starting point here will be the balanced chemical equation for this combustion reaction
4
P
(s]
+
5
O
2(g]
→
2
P
2
O
5(s]
Notice that you have a
4
:
5
mole ratio between phosphorus and oxygen. This means that, regardless of how many moles of phosphorus you have, the reaction will always need
5
4
time more moles of oxygen gas.
Use phosphorus' molar mass to determine how many moles you have in that
93.0-g
sample
93.0
g
⋅
1mole P
30.974
g
=
3.0025 moles P
Use the aforementioned mole ratio to determine how many moles of oxygen you would need for many moles of phosphorus to completely take part in the reaction
