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

2HClH2+Cl2

Notice that you have a 2:1 mole ratio between HCl and Cl2, 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 g1 mole36.5 g=1.92 moles

As a result, the number of Cl2 moles is

nCl2=nHCl2=1.922=0.96 moles

At STP, 1 mole of any ideal gas occupies 22.4 L, which means that the volume of Cl2 produced will be

n=VVmolarV=nVmolar=0.96 moles22.4 Lmole=21.5 L