IChO Preparatory Problems — Sample
IChO 2023 (Zurich) Preparatory Problem 2

Atmospheric Carbon Capture

Physical Chemistry — Thermodynamics16 pts
Problem Context

Direct air capture (DAC) of CO₂ involves the reaction of CO₂ with a solid sorbent such as calcium oxide. Reaction 1: CaO(s) + CO₂(g) → CaCO₃(s) ΔH°₁ = −178.3 kJ/mol Reaction 2: CaCO₃(s) → CaO(s) + CO₂(g) ΔH°₂ = +178.3 kJ/mol Thermodynamic data at 298 K: CaO(s): ΔGf° = −604.0 kJ/mol, S° = 39.8 J/mol·K CaCO₃(s): ΔGf° = −1128.8 kJ/mol, S° = 91.7 J/mol·K CO₂(g): ΔGf° = −394.4 kJ/mol, S° = 213.8 J/mol·K

A

Calculate ΔG° for Reaction 1 at 298 K.

3 pts
B

Calculate ΔS° for Reaction 1 at 298 K and comment on its sign.

3 pts
C

Estimate the temperature at which Reaction 1 becomes thermodynamically unfavorable (ΔG° > 0). State any assumptions.

4 pts
D

In the industrial calcination step, CaCO₃ is heated to release pure CO₂. Explain why this release temperature (from part c) is industrially significant and what it implies for the energy cost of a CaO-based DAC cycle.

3 pts
E

A 1.00 kg sample of CaO is used to capture CO₂ at 298 K. Assuming 100% conversion, calculate the mass of CO₂ captured.

3 pts