Test 7

Problems

1) Using Hess’s law calculate the enthalpy of formation for:

PCl₅(g) + H₂O(g) -> POCl₃(g) + 2HCl(g)

And given the following:

P(white) + 3/2Cl₂(g) + 1/2O₂(g) -> POCl₃(g); ΔH^o = -558.5kJ/mol

H₂(g) + Cl₂(g) -> 2HCl(g); ΔH^o = -184.6kJ/mol

PCl₅(g) -> P(white) + 5/2Cl₂(g); ΔH^o = +374.9kJ/mol

H₂O(g)-> H₂(g) + 1/2O₂(g); ΔH^o = +241.8kJ/mol

2)Using the standard enthalpies of formation calculate the ΔH^o for the reduction of ferric oxide by aluminum at 25 ^oC

2Al + Fe₂O₃ -> 2Fe + Al₂O₃; ΔH^o = ?

http://en.wikipedia.org/wiki/Standard_enthalpy_change_of_formation_%28data_table%29

Answers

1) PCl₅(g) + H₂O(g) -> POCl₃(g) + 2HCl(g); ΔH^o = -126.4kJ/mol

2) ΔH^o = (sum of the nΔH^o_f products) – (sum of the nΔH^o_freactants)

ΔH^o = (-1669.8) – (-826) = -843.8 kJ/mol