Answer:
2.52 g H₂
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.
<u>(Step 1)</u>
The unbalanced equation:
Ca(s) + H₂O(l) ----> Ca(OH)₂(aq) + H₂(g)
<u>Reactants</u>: 1 calcium, 2 hydrogen, 1 oxygen
<u>Products</u>: 1 calcium, 4 hydrogen, 2 oxygen
The balanced equation:
1 Ca(s) + 2 H₂O(l) ----> 1 Ca(OH)₂(aq) + 1 H₂(g)
<u>Reactants</u>: 1 calcium, 4 hydrogen, 2 oxygen
<u>Products</u>: 1 calcium, 4 hydrogen, 2 oxygen
<u>(Step 2)</u>
Molar Mass (H₂): 2(1.008 g/mol)
Molar Mass (H₂): 2.016 g/mol
<u>(Step 3)</u>
2.50 moles H₂O 1 mole H₂ 2.016 g
--------------------------- x ------------------------- x ---------------------- = 2.52 g H₂
2 moles H₂O 1 mole