Question

What is the standard free energy decomposition for potassium chlorate? (Note: Potassium chlorate decomposes into potassium chloride and oxygen.)

(a) -79.8 kj/mol

(b) -99.4 kj/mol

(c) -39.9 kj/mol

(d) -44.8 kj/mol

(e) -49.7 kj/mol

Answer 1

The decomposition reaction is:

2 KClO₃ (s) → 2KCl (s) + 3O₂ (g)

[2ΔH_f(KCl (s)) + 3ΔH_f(O₂ (g))] - [2ΔH_f(KClO₃ (s))]

The ΔH_f of the reaction is taken from the standard tables.
[2(-435.89) + 3(0)] - [2(-391.2)] = -89.38 kJ

The nearest answer is d