Mole ratios and reactions

Question

How many grams of NO are required completely to react with 15.0 L O2 gas at STP? Be sure to use coefficients.

Answer 1

At STP 1 mol of gas = 22.4 L (memorize this)

Reaction taking place is 2NO + O₂ ==> 2NO₂

moles O2 present = 15.0 L x 1 mol/22.4 L = 0.670 moles O2

moles NO needed = 0.670 moles O2 x 2 moles NO / mole O2 = 1.34 moles NO needed