Problem: Use tabulated half-cell potentials to calculate ΔG°rxn for each of the following reactions at 25 °C.O2(g) + 2H2O(l) + 2Cu(s) → 4OH−(aq) + 2Cu2+(aq) Express the energy change in kilojoules to one significant figure.

FREE Expert Solution

We are asked to calculate ΔG°rxn for each of the following reactions at 25 °C.


O2(g) + 2H2O(l) + 2Cu(s) → 4OH(aq) + 2Cu2+(aq)


The relationship between ΔG and Ecell is


G=-nFEcell



Step 1. Write the two half-cell reactions

O2(g) + 2 H2O(l) → 4OH(aq)

Cu(s) → 2Cu2+(aq)


Step 2. Identify the oxidation half-reaction (anode) and the reduction half-reaction (cathode)

When a balanced reaction is given, identify the anode and the cathode half-reactions by determining the changes in oxidation states of each species based on the given reaction:

Recall:

Lose               Gain
Electron         Electrons
Oxidation       Reduction

cathode → reduction → oxidation number decreases

anode → oxidation → oxidation number increases

For ions: charge of the ion = oxidation number
For neutral atoms/compound: oxidation number = 0


Cu(s) →  2Cu2+(aq)
oxidation number increased → lost electrons → oxidized anode


O2(g) + 2 H2O(l) → 4OH(aq)
oxidation number decreased reduced → cathode


Step 3. Determine the half-cell potentials (refer to the Standard Reduction Potential Table)

2 Cu(s) → 4 e- + 2Cu2+(aq)                                        E°cell = 0.342 V

O2(g) + 2 H2O(l) + 4 e-→ 4OH(aq)                            E°cell = 0.401 V


Step 4. Calculate E°cell.

E°cell=E°cathode-E°anodeE°cell=0.401 V -0.342 V  

  E°cell = 0.059 V


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Problem Details

Use tabulated half-cell potentials to calculate ΔG°rxn for each of the following reactions at 25 °C.

O2(g) + 2H2O(l) + 2Cu(s) → 4OH(aq) + 2Cu2+(aq) 

Express the energy change in kilojoules to one significant figure.