The most common method of producing bromine involves oxidizing bromine ions (Br^-) to bromine liquid (Br2) using chlorine gas (Cl2). What is the E for this reaction?
To determine the standard reduction potential (E°) for the reaction, we need to use the standard reduction potentials for the half-reactions involved.
The reduction half-reaction for the oxidation of bromide ions (Br^-) to bromine liquid (Br2) is:
Br^- (aq) → Br2 (l) + 2e^-
The standard reduction potential for this half-reaction can be found in a table. Using the values, we find that the standard reduction potential for this half-reaction is +1.09 V.
The reduction half-reaction for the reduction of chlorine gas (Cl2) to chloride ions (Cl^-) is:
Cl2 (g) + 2e^- → 2Cl^- (aq)
The standard reduction potential for this half-reaction is +1.36 V.
To calculate the overall standard reduction potential for the reaction, we can subtract the reduction potential of the oxidation half-reaction from the reduction potential of the reduction half-reaction:
E° = (+1.36 V) - (+1.09 V)
E° = +0.27 V
Therefore, the standard reduction potential (E) for this reaction is +0.27 V.
To find the standard reduction potential (E) for the given reaction, we need to look up the reduction potentials (E°) for both half-reactions involved and then apply the Nernst equation. The half-reactions involved are:
1. Oxidation half-reaction: Br^-(aq) → Br2(l) + 2e^-
2. Reduction half-reaction: Cl2(g) + 2e^- → 2Cl^-(aq)
First, let's find the E° values for these half-reactions. The reduction potentials can be found in tables or reference materials. The values at 25°C (298 K) are approximately:
E°(Br^-(aq) → Br2(l) + 2e^-) = +1.09 V
E°(Cl2(g) + 2e^- → 2Cl^-(aq)) = +1.36 V
Now, since the desired reaction involves oxidation of Br^-(aq) and reduction of Cl2(g), we need to reverse the reduction half-reaction. By doing so, we also need to change the sign of its reduction potential:
Reversed reduction half-reaction: 2Cl^-(aq) → Cl2(g) + 2e^-
E°(reversed reduction) = -E°(reduction) = -1.36 V
Now, we can write the overall balanced equation of the desired reaction:
2Br^-(aq) + Cl2(g) → Br2(l) + 2Cl^-(aq)
To calculate the overall E° for this reaction, we sum the E° values of the individual half-reaction:
E°(overall) = E°(oxidation) + E°(reversed reduction)
E°(overall) = 1.09 V + (-1.36 V)
E°(overall) = -0.27 V
Therefore, the standard reduction potential (E°) for the given reaction is approximately -0.27 V.
See your first two problems. Same solutions.
Post your work if you get stuck.