Answer:
2.52 g H₂
Step-by-step explanation:
To find the mass of hydrogen gas, you need to (1) convert moles H₂O to moles H₂ (via mole-to-mole ratio from reaction coefficient) and then (2) convert moles H₂ to grams H₂ (via molar mass from periodic table values). When multiplying the given value by the mole-to-mole ratio, you need to use the coefficients of the balanced equation. An reaction is balanced once there is an equal amount of each element on both sides.
(Step 1)
The unbalanced equation:
Ca(s) + H₂O(l) ----> Ca(OH)₂(aq) + H₂(g)
Reactants: 1 calcium, 2 hydrogen, 1 oxygen
Products: 1 calcium, 4 hydrogen, 2 oxygen
The balanced equation:
1 Ca(s) + 2 H₂O(l) ----> 1 Ca(OH)₂(aq) + 1 H₂(g)
Reactants: 1 calcium, 4 hydrogen, 2 oxygen
Products: 1 calcium, 4 hydrogen, 2 oxygen
(Step 2)
Molar Mass (H₂): 2(1.008 g/mol)
Molar Mass (H₂): 2.016 g/mol
(Step 3)
2.50 moles H₂O 1 mole H₂ 2.016 g
--------------------------- x ------------------------- x ---------------------- = 2.52 g H₂
2 moles H₂O 1 mole