finding grams of P from stp?

Question

How many grams of phosphorus react with 39.4 L of O2 at STP to form tetraphosphorus decaoxide?
P4(s) + 5 O2(g) P4O10(s)

Answer 1

STP means Standard Temperature and Pressure, a scientific term which represents a convention of designating standard conditions. Often, but not always, denoting a temperature of 0 °C and pressure of 101.325 kPa (1 atm).
With the ideal gas equation PV = nRT, we find for O2:
n = 1*39.4/0.08206*273 = 1.76
From the reaction equation, we know that 5 Mol of O2 is needed to react with 1 Mol of P4, with formula weight of 123.9. Hence the answer is:
123.9n/5 = 43.6 (grams)