Calculate change in reaction

Question

Given that

H2(g)+F2(g)⟶2HF(g)    ΔH∘rxn=−555⋅4kJmol

2H2(g)+O2(g)⟶2H2O2(l)    ΔH∘rxn=−572⋅4kJmol

Calculate the value of ΔH∘rxn for 

2F2(g)+2H2O2(l)⟶4HF(g)+O2(g) 

Answer 1

HESS' LAW

2F₂ + 2H₂O ==> 4HF + O₂ TARGET EQUATION

(1) H2 + F2 ==> 2HF ... ∆H = -555.4 kJ/mol

(2) 2H2 + O2 ==> 2H2O ... ∆H = -572.4 kJ/mol

Prodedure:

copy (1) x 2: 2H2 + 2F2 ==> 4HF ... ∆H = 2 x -555.4 = -1110.8 kJ/mol

reverse (2): 2H2O ==> 2H2 + O2 ... ∆H = +572.4 kJ/mol

Add them:

2H2 + 2F2 + 2H2O ==> 4HF + 2H2 + O2

Combine and cancel like terms to get ...

2F2 + 2H2O ==> 4HF + O2 TARGET EQUATION

∆H = -1110.8 + 572.4

∆H = -538.4 kJ/mol