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"