How many moles of hydrogen, H2, are needed to react with 2.0 moles of nitrogen, N2

The coefficients DO NOT represent mass. Moles to mole ratios in a balanced chemical reaction are equivalents. Example 1: 3 H2 (g) + N2 (g) → 2 NH3 (g) tells us that 1 mole of nitrogen will stoichiometrically react with 3 moles of hydrogen to theoretically (ideally) produce 2 moles of ammonia.