Question

The destruction of the ozone layer by chlorofluorocarbons (CFC’s) can be described by the following reactions:

ClO(g) + O3(g) ? Cl(g) + 2 O2(g) ?H°rxn = –29.90 kJ

2 O3(g) ? 3 O2(g) ?H°rxn = 24.18 kJ

Determine the value of heat of reaction for the following:
Cl(g) + O3(g) ? ClO(g) + O2(g) ?H°=?

Answer 1

The given reactions are:

  (1)      ClO(g) + O₃(g)   ---->    Cl(g) + 2 O₂ (g)    ΔH°_rxn = –29.90 kJ
(2)                    2 O₃(g)   ---->    3O₂ (g)                 ΔH°_rxn = +24.18 kJ

The reverse reaction of (1) will be:

  (3)       Cl(g) + 2 O₂ (g)   ----> ClO(g) + O₃(g)    ΔH°_rxn = +29.90 kJ

(2) + (3) gives:

                           2 O₃(g)   ---->    3O₂ (g)                 ΔH°_rxn = +24.18 kJ
              Cl(g) + 2 O₂ (g)   ----> ClO(g) + O₃(g)     ΔH°_rxn = +29.90 kJ

         ------------------------------------------------------------------------

               Cl(g)   +  O₃(g)   ---->    ClO(g) + O₂ (g)  ΔH°_rxn = +54.08 kJ

So the value of heat of reaction for desired reaction is 54.08 kJ.