According to the following reaction, how many grams of hydrogen gas will be formed upon the complete reaction of 31.7 grams of hydrobromic acid?

Question

hydrobromic acid (aq) hydrogen (g) + bromine (l)

Answer 1

2HBr (aq) = H₂(g) + Br₂(g)

molar mass of HBr = (1 + 79.9) g/mol = 80.9 g/mol

moles of HBr = mass/molar mass = 31.7/80.9 = 0.392 moles

2 moles of HBr produce 1 moles of H₂. So, 0.392 moles produce (0.392 * 1/2) moles or 0.196 moles of H₂.

mass of H₂ = moles * molar mass = 0.196 moles * 2 g/mol = 0.392 g