Question

One reaction of iron with hydrochloric acid is represented by the following thermochemical equation.
Fe(s) + 2HCl(aq)  FeCl2(aq) + H2(g); H°= –87.9 kJ
How much heat is liberated at constant pressure if 0.680 g of iron reacts with 49.8 mL of 0.661 M HCl?

A) 1.07 kJ

B) 6.86 kJ

C) 1.45 kJ

D) 87.9 kJ

E) 59.8 kJ

Answer 1

Fe(s) + 2HCl(aq)  FeCl2(aq) + H2(g); H°= –87.9 kJ

no of moles of Fe = W/G.A.Wt

                               = 0.68/56   = 0.012moles

no of moles of HCl     = molarity * volume in L

                                    = 0.661*0.0498   = 0.0329moles

1 mole of Fe react with 2 moles of HCl

0.012 moles of Fe react with = 2*0.012/1 = 0.024 moles of HCl

HCl is excess reagent

Fe is limiting reagent

Fe(s) + 2HCl(aq)  FeCl2(aq) + H2(g); H°= –87.9 kJ

1 mole of Fe react with HCl to gives -87.9KJ enegy

0.012 moles of Fe react with HCl to gives = -87.9*0.012/1   = -1.0548KJ

A) 1.07 kJ