12.4 g of phosphorus reacts with 9.6 g of oxygen. Which of the following chemical equation represents this reaction?
[Relative atomic mass: P, 31; 0, 16]
A P + O2 + PO2
B 2 P + O2 + 2 PO
C 3P +2 02 → P304
D 4P +3 02 → 2 P203

D 4P +3O₂ → 2 P₂O₃

Explanation:

In this problem, we need to convert the mass of phosphorus and oxygen to moles trying to find the ratio of reaction (The moles of P that reacts per mole of O₂):

Moles P:

12.4g P * (1mol P / 31g) = 0.4 moles

Moles O₂:

9.6g * (1mol / 32g) = 0.3 moles

The ratio of reaction is:

0.4 mol / 0.3 mol = 1.33 = 4 moles of P / 3 moles of O₂

That means 4 moles of P react with 3 moles of O₂ and the reaction that represents this ratio is:

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"