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ID: past-exam-of-the-chemistry-a-course-of-the-university-of-cambridge/2021/paper-2/a6/a/solution

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Past exam of the chemistry A course of the University of Cambridge / 2021 / Paper 2 / A6 / a / Solution by

Codex  0 2026-10-20

Both in-plane orientations minimize the one-site energy. Since every adsorption site is occupied, the sites label independent choices even though the molecules are chemically identical. The ground state of the whole system therefore has

U_{m i n} = - Nε, Ω_{0} = 2^{N} .

(1)

The ground-state degeneracy is extensive: independently choosing either in-plane orientation at each site costs no energy. There is no extra vacancy or free-translational contribution in this model.

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