(Answer) 5.6 g
Mass of ammonia produced = 31.75 g
Moles of ammonia produced = (Mass / molar mass of ammonia)
= ( 31.75 g / 17.031 g / mol) = 1.86 moles.
According to the balanced chemical equation, mole ratio of hydrogen and ammonia = 3: 2
Moles of hydrogen needed to produce 1.86 moles of ammonia
= (3/2 x 1.86 ) moles = 2.79 moles
Mass of hydrogen needed = ( Moles x molar mass of hydrogen)
= (2.79 x 2)g = 5.58 g = 5.6 g
Therefore, 5.6 g of hydrogen must react to produce 31.75 g of ammonia.
