How many grams of H2 are needed to react with 2.70 g of N2?

3H₂ + N₂ → 2NH₃

mole of N₂ = mass : molar mass

= 2.70g : (14 * 2)

= 0.096 mol

mole ratio of N₂ : H₂

1 : 3

∴ if the moles of N₂ = 0.096 mol

then the mole of H₂ = 0.096 mol * 3

= 0.289 mol

Now, mass = mole * molar mass

∴ mass of H₂ needed to react = 0.289 mol * (1 * 2)

= 0.579 g