How many grams of P2O5 will be produced from 125 g of P?

Answer 1

From every two atoms of P, one molecule of P2O5 is formed. The relative formula mass of two atoms of P (phosphorous) is 62, whereas for one molecule of P2O5 it is 142. The mass of P2O5 formed is therefore 142/62 times the mass of P we started with. This comes out to 286.3g (to one decimal place).

Answer 2

The molar mass of P2O5 is 141.94 g/mol. The molar ratio between P and P2O5 is 2:1. Therefore, 125 g of P will produce 125/31.00 = 4.032 moles of P. Since the molar ratio is 2:1, this will produce 2.016 moles of P2O5. Finally, 2.016 moles of P2O5 is equal to 2.016 * 141.94 = 286.69 grams.