Question

# Phosphorus reacts with oxygen to form diphosphorus 4P(s)+5O2(g)⟶2P2O5(s) How many grams of P2O5 are formed when 7.65 g of phosphorus reacts with excess oxygen? Show the unit analysis used for the calculation by placing the correct components into the unit-factor slots.

Answer

13.2 g P2O5

- Q: What is the equation for the reaction? A: 4P(s) + 5O2(g) -> 2P2O5(s)
- Q: What is the molar mass of P2O5? A: Molar mass of P2O5 = 2 x (30.97 g/mol) + 5 x (16.00 g/mol) = 141.94 g/mol.
- Q: What is the mole ratio of P2O5 to P? A: From the balanced chemical equation, 4 moles of P form 2 moles of P2O5.
- Q: What is the amount of P2O5 formed? A: 7.65 g P x (1 mol P / 30.97 g P) x (2 mol P2O5 / 4 mol P) x (141.94 g P2O5 / 1 mol P2O5) = 13.2 g P2O5.