You have .8 liters of a 0.5M HCl solution. If you use this solution to complete a decomposition reaction of HCl how many moles of hydrogen (H2) would be produced?
2HCl ==> H2 + Cl2
mols HCl = M x L
mols H2 = 1/2 mols HCl (from the coefficients in the balanced equation.)