How many liters of hydrogen gas are produced at STP from the decomposition of #"70.0 g"# of hydrogen chloride?

1 Answer
Jan 18, 2015

The answer is #"21.5 L" #.

So, start with the balanced chemical equation for the decomposition of hydrochloric acid

#2"HCl" -> "H"_2 + "Cl"_2#

Notice that you have a #"2:1"# mole ratio between #"HCl"# and #"Cl"_2#, which means that every 2 moles of the former will produce 1 mole of the latter. The number of moles of #"HCl"# you have is

#"70.0 g" * ("1 mole")/("36.5 g") = 1.92# #"moles"#

As a result, the number of #"Cl"_2# moles is

#n_(Cl_2) = n_(HCl)/2 = 1.92/2 = 0.96# #"moles"#

At STP, 1 mole of any ideal gas occupies 22.4 L, which means that the volume of #"Cl"_2# produced will be

#n = V/V_("molar") => V = n * V_("molar") = 0.96# #"moles" * 22.4# #L/("mole") = 21.5# #"L"#