Calcium hydride reacts with water to form calcium hydroxide and hydrogen gas. The balanced equation to this is #CaH_2+2H_2O#----#Ca(OH)_2+2H_2# How many grams of calcium hydride are needed to form 8.400 g of hydrogen?

1 Answer

Answer:

You need #"87.69 g of CaH"_2# to form #"8.400 g of H"_2#.

Explanation:

There are four steps to answering this type of stoichiometry problem.

  1. Write the balanced equation for the reaction.
  2. Use the molar mass of #"H"_2# to convert grams of #"H"_2# to moles of #"H"_2#.
  3. Use the molar ratio from the balanced equation to convert moles of #"H"_2# to moles of #"CaH"_2#.
  4. Use the molar mass of #"CaH"_2# to convert moles of #"CaH"_2# to grams of #"CaH"_2#.

Step 1. Write the balanced equation.

#"CaH"_2 + "2H"_2"O" → "Ca(OH)"_2 + "2H"_2#

Step 2. Convert grams of #"H"_2# to moles of #"H"_2#.

The molar mass of #"H"_2# is 2.016 g/mol.

#8.400 cancel("g H"_2) × ("1 mol H"2)/(2.016 cancel("g H"2)) = "4.1667 mol H"_2#

Step 3. Use the molar ratio to calculate the moles of #"CaH"_2#.

From the balanced equation, the molar ratio is #"1 mol CaH"_2:"2 mol H"_2#.

#4.1667 cancel("mol H"_2) × ("1 mol CaH"_2)/(2 cancel("mol H"_2)) = "2.0833 mol CaH"_2#

Step 4. Convert moles of #"CaH"_2# to grams of #"CaH"_2#.

The molar mass of #"CaH"_2# is 42.09 g/mol.

#2.0833 cancel("mol CaH"_2) × ("42.09 g CaH"_2)/(1 cancel("mol CaH"_2)) = "87.69 g CaH"2#

The reaction requires #"87.69 g CaH"_2#.

This video link allows you to furthur practice similar problems.