Problem: Use tabulated half-cell potentials to calculate ΔG°rxn for each of the following reactions at 25 °C.Br2(l) + 2I−(aq) → 2Br−(aq) + I2(s) Express the energy change in kilojoules to two significant figures.

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

Br2(l) + 2I(aq) → 2Br(aq) + I2(s) 

cathode → reduction → oxidation number decreases

anode → oxidation → oxidation number increases


Half cell reactions: 

Br2(l) + 2 e- → 2Br(aq)          E°cell = 1.087 V → cathode

2I(aq) + 2 e-→ I2(s)               E°cell = 0.536 V → anode


 Calculate E°cell.

E°cell=E°cathode-E°anodeE°cell=1.087 V -0.536 V  

  E°cell = 0.551 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.

Br2(l) + 2I(aq) → 2Br(aq) + I2(s) 

Express the energy change in kilojoules to two significant figures.