The following reactions all occur in a blast furnace. Which of these are redox reactions?

(a) 3Fe2 O3 (s) + CO (g) ⟶ 2Fe3 O4 (s) + CO2 (g)

b) Fe3 O4 (s) + CO (g) ⟶ 3FeO (s) + CO2 (g)

c) FeO (s) + CO (g) ⟶ Fe (l) + CO2 (g)

d) C (s) + O2 (g) ⟶ CO2 (g)

e) C (s) + CO2 (g) ⟶ 2CO (g)

f) CaCO3 (s) ⟶ CaO (s) + CO2 (g)

g) CaO (s) + SiO2 (s) ⟶ CaSiO3 (l)

The redox reactions are: (a) 3Fe₂O₃ (s) + CO (g) ⟶ 2Fe₃O₄ (s) + CO₂ (g)

b) Fe₃O₄ (s) + CO (g) ⟶ 3FeO (s) + CO₂ (g)

c) FeO (s) + CO (g) ⟶ Fe (l) + CO₂ (g)

d) C (s) + O₂ (g) ⟶ CO₂ (g)

e) C (s) + CO₂ (g) ⟶ 2CO (g)

Explanation:

Redox reaction is a type of chemical reaction that involves the simultaneous transfer of electrons and change in the oxidation state.

The chemical species that accepts electrons and gets reduced is called an oxidizing agent. Whereas, chemical species that loses electrons and gets oxidized is called a reducing agent.

(a) 3Fe₂O₃ (s) + CO (g) ⟶ 2Fe₃O₄ (s) + CO₂ (g)

In this reaction, Fe accepts electrons and gets reduced from + 3 oxidation state in Fe₂O₃ to + 8/3 (+2.66) oxidation state in Fe₃O₄. Whereas, C loses electrons and gets oxidized from + 2 oxidation state in CO to + 4 oxidation state in CO₂.

Therefore, it is a redox reaction.

b) Fe₃O₄ (s) + CO (g) ⟶ 3FeO (s) + CO₂ (g)

In this reaction, Fe accepts electrons and gets reduced from + 8/3 (+2.66) oxidation state in Fe₃O₄ to + 2 oxidation state in FeO. Whereas, C loses electrons and gets oxidized from + 2 oxidation state in CO to + 4 oxidation state in CO₂.

Therefore, it is a redox reaction.

c) FeO (s) + CO (g) ⟶ Fe (l) + CO₂ (g)

In this reaction, Fe accepts electrons and gets reduced from + 2 oxidation state in FeO to 0 oxidation state in Fe. Whereas, C loses electrons and gets oxidized from + 2 oxidation state in CO to + 4 oxidation state in CO₂.

Therefore, it is a redox reaction.

d) C (s) + O₂ (g) ⟶ CO₂ (g)

In this reaction, O accepts electrons and gets reduced from 0 oxidation state in O₂ to - 2 oxidation state in CO₂. Whereas, C loses electrons and gets oxidized from 0 oxidation state in C to + 4 oxidation state in CO₂.

Therefore, it is a redox reaction.

e) C (s) + CO₂ (g) ⟶ 2CO (g)

In this reaction, C accepts electrons and gets reduced from + 4 oxidation state in CO₂ to + 2 oxidation state in CO. Whereas, C loses electrons and gets oxidized from 0 oxidation state in C to + 2 oxidation state in CO.

Therefore, it is a redox reaction.

f) CaCO₃ (s) ⟶ CaO (s) + CO₂ (g)

The oxidation states of Ca, C and O; in the reactant and products are + 2, + 4 and - 2, respectively. Thus the oxidation states of all the elements in this reaction remains same.

Therefore, it is NOT a redox reaction.

g) CaO (s) + SiO₂ (s) ⟶ CaSiO₃ (l)

The oxidation states of Ca, Si and O; in the reactant and products are + 2, + 4 and - 2, respectively. Thus the oxidation states of all the elements in this reaction remains same.

Therefore, it is NOT a redox reaction.