Magnesium metal (0.100 mol) and a volume of aqueous hydrochloric acid that contains 0.500 mol of HCl are combined and react to completion. How many liters of hydrogen gas, measured at STP, can be produced? #"Mg"(s) + 2"HCl"(aq) -> "MgCl"_2(aq) + "H"_2(g)#

1 Answer
Bio
May 7, 2016

#2.24 "L"#

Explanation:

Step 1: determine the reaction

The chemical equation is already given.

#"Mg" + 2 "HCl" -> "MgCl"_2 + "H"_2#

Step 2: determine which reactant is limiting

0.100 mol of Mg reacts with 0.500 mol of HCl, which of them will run out first?

From the reaction, the ratio of #"Mg"# to #"HCl"# used is #1:2#. This means that if the reaction goes to completion, the #0.100 "mol"# of #"Mg"# will react with #0.100 "mol" xx 2 = 0.200 "mol"# of #"HCl"#. This leaves #0.500 "mol" - 0.200 "mol" = 0.300 "mol"# of #"HCl"#.

Step 3: determine how much #"H"_2# is produced.

#0.100 "mol"# of #"Mg"# and #0.200 "mol"# of #"HCl"# will produce #0.100 "mol"# of #"H"_2#.

Step 4: determine the volume at STP

Each mole of ideal gas occupies #22.4 "L"# at STP. Therefore, #0.100 "mol"# of #"H"_2# will occupy #2.24 "L"# of space.

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