Question

Write the balanced half-reaction for the following redox reaction (include physical states like I did in final answer):

2CO₂(g) + 12H⁺(aq) + 6Zn(s) -----> C₂H₅OH(l) + 3H₂O(l) + 6Zn²⁺(aq)

Answer 1

First, define the “ACIDIC” solution/conditions as H+ presence and

Basic solution implies OH- once it is balanced.

Also; note that ALL species must be balanced, as well as charges

Typical steps:

1) split half redox cells

CO2 = C2H5OH

Zn = Zn+2

2) balance atoms other than O,H

2CO2 = C2H5OH

Zn = Zn+2

3) balance O by adding H2O

2CO2 = C2H5OH + 3H2O

Zn = Zn+2

4) balance H by adding H+

12H+ + 2CO2 = C2H5OH + 3H2O

Zn = Zn+2

5) balance charge by adding e-

12e- + 12H+ + 2CO2 = C2H5OH + 3H2O

Zn = Zn+2 + 2e-

6) balance e- by multiplying by the Greatest common divisor

12e- + 12H+ + 2CO2 = C2H5OH + 3H2O

6Zn = 6Zn+2 + 12e-

7) Add both equations

6Zn + 12e- + 12H+ + 2CO2 = C2H5OH + 3H2O  + 6Zn+2 + 12e-

8) simplify repeating elements, H+, H2O, and e- typically

6Zn + 12H+ + 2CO2 = C2H5OH + 3H2O  + 6Zn+2

therefore, half reactions are:

12e- + 12H+(aq) + 2CO2(g) = C2H5OH(l) + 3H2O(l)

6Zn(s) = 6Zn+2(aq) + 12e-