Question

Potassium chlorate (KClO3) is often used to generate oxygen according to its decomposition reaction (shown below):

2KClO3(s) --> 2KCl(s) + 3O2(g)

Use the thermochemical data to calculate the standard change in Gibbs Energy (rGʅ) for this reaction at a temperature of 298K.

Answer 1

When 2 mole of potassium chlorate decompose to give 2 mole of KCl & 3 mole of oxygen

The reaction is

2KClO3---------> 2KCl + 3 O2

Therefore gibbs free energy of the reaction can be calculated by using standard formation constant

ΔG⁰_f = ΔG⁰(formation of product – reactant)

           = 2 ΔG⁰_f KCl (s) + 3 ΔG⁰_f O2(g) - 2 ΔG⁰_f KClO3(s)

From thermodynamic data

ΔG⁰_f KCl (s)         = -408.5kJ/mol

ΔG⁰_f O2(g)          = 0

ΔG⁰_f KClO3(s)     = -296.31 kJ/mol

We can substitute all the value in the above formula

ΔG⁰_f = (2 x -408.5) +( 3 x 0 ) – (2 x – 296.31)

          = -817 + 0 + 529. 62

           = -224.38 kJ/mol