What mass of phosphorus oxide (5) is formed during the combustion of phosphorus weighing 124 g?

Let’s compose the equation of the phosphorus combustion reaction:
4P + 5O2 = 2P2O5;

The molecular weight of phosphorus is 31 g / mol. Let’s find the amount of substance in phosphorus:
124/31 = 4 mol;

Let’s find the molecular weight of phosphorus oxide:
31 * 2 + 16 * 5 = 142 g / mol;

Before phosphorus oxide there is a coefficient that is 2 times less than before phosphorus. This means that the amount of substance in the oxide is 2 mol. Let’s find the mass of phosphorus oxide:
142 * 2 = 284 grams;

Answer: The mass of phosphorus oxide is 284 grams.