Answer:
B.) 36.0 grams
Explanation:
To find the mass of water, you need to (1) convert grams H₂ to moles (using the molar mass), then (2) convert moles H₂ to moles H₂O (using mole-to-mole ratio from reaction coefficients), and then (3) convert moles H₂O to grams (using the molar mass). It is important to arrange the conversions in a way that allows for the cancellation of units.
Molar Mass (H₂): 2(1.008 g/mol)
Molar Mass (H₂): 2.016 g/mol
Molar Mass (H₂O): 2(1.008 g/mol) + 15.998 g/mol
Molar Mass (H₂O): 18.014 g/mol
2 H₂ + O₂ -----> 2 H₂O
^ ^
4.0 g H₂ 1 mole 2 moles H₂O 18.014 g
--------------- x ---------------- x ------------------------ x --------------- = 36 g H₂O
2.016 g 2 moles H₂ 1 mole
