Question

From the reaction NH3 + 2O2 → HNO3 + H2O, how many molecules of oxygen gas are required to react completely with 68 grams of ammonia (NH3)?

Answer 1

equation is already balanced so go straight to the stoich

start with 68g of ammonia

1. divide by molar mass of ammonia to get moles of ammonia
2. since 1 mol NH3 = 2 mol O2 (going by the equation), multiply moles of ammonia by 2 to get moles of O2
3. multiply moles of O2 by Avogadro's # to get molecules