Stoichiometry question

Question

Phosphorus will burn in oxygen to give diphosphorus pentoxide. How many grams of phosphorus can be burned to produce the diphosphorus pentoxide if 100.0 g of oxygen are available to be used?

Answer 1

Write the correctly balanced equation for the reaction taking place:

P₄ + 5O₂ ==> P₄O₁₀ (P₄O₁₀ is the same as P₂O₅ but P doesn't exist as such in nature so we use P₄)

Using only 100.0 g of O2, we can find how many grams of P4 can be burned. For this, we use the balanced equation:

100.0 g O2 x 1 mole O2/32 g = 3.125 moles O2

moles P4 = 3.125 moles O2 x 1 mole P4/5 moles O2 = 0.625 moles P4

grams P4 = 0.625 moles P4 x 123.896 g/mole = 77.44 g

If you were to use the more simplified equation 4P + 5O2 ==> 2P2O5 and conduct the calculations....

100.0 g O2 x 1 mol/32 g x 4 mol P/5 mol O2 x 30.974 g/mol = 77.44 g (same answer as above)