Q3(c). Thermodynamics of the H₂–O₂ fuel cell
Consider the reaction H₂(g) + ½O₂(g) → H₂O(l), which occurs in a H₂–O₂ fuel cell. (i) Identify the elements that undergo oxidation and reduction. (ii) Calculate the standard reaction Gibbs free energy (ΔrG°) at 25 °C. (iii) Write down the two reduction half-reactions for the cell. (iv) Calculate the Ecell. Given: ΔfH°(H₂O, l) = −285.83 kJ mol⁻¹; S°ₘ(H₂O, l) = 69.91 J K⁻¹ mol⁻¹; S°ₘ(H₂, g) = 130.68 J K⁻¹ mol⁻¹; S°ₘ(O₂, g) = 205.14 J K⁻¹ mol⁻¹.
Answer in brief
Hydrogen is oxidised (0 → +1) and oxygen reduced (0 → −2); ΔrG° = −237.13 kJ mol⁻¹; O₂ + 4H⁺ + 4e⁻ → 2H₂O and 2H⁺ + 2e⁻ → H₂; E°cell = 1.23 V.
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Covershydrogen–oxygen fuel cellGibbs energycell EMFhalf-reactionsthermodynamic efficiency
All parts of Question 3
- 3(a) Electronic and molecular geometry of BrF₅ and [ICl₂]⁻10 marks
- 3(b) Reading a one-component phase diagram20 marks
- 3(c) Thermodynamics of the H₂–O₂ fuel cell20 marks