Q.(a) List the characteristics of Gibbs free Energy.

This choice question asks either for the characteristics of Gibbs free energy, or for a comparison of H2O and H2O2 structures with the deuterium exchange reaction. …

This is a 5-mark either/or question; both alternatives are answered below.

PART (a) — Characteristics of Gibbs free energy (G):

1. It is a thermodynamic state function — its change depends only on the initial and final states, not the path.
2. It is an extensive property (depends on the amount of substance) and has the units of energy (J or kJ).
3. It is defined as G = H - TS (H = enthalpy, T = absolute temperature, S = entropy).
4. Its change at constant T and P is ΔG = ΔH - TΔS.
5. It is the criterion of spontaneity: ΔG < 0 → spontaneous (feasible); ΔG = 0 → system at equilibrium; ΔG > 0 → non-spontaneous.
6. The decrease in Gibbs free energy equals the maximum useful (non-expansion/net) work obtainable from a process: -ΔG = W(max, useful).
7. It is related to the equilibrium constant by ΔG° = -RT ln K.

PART (b)(i) — Structures of H2O and H2O2:

• H2O (water): a bent/angular molecule; the oxygen is sp3 hybridised with two bond pairs and two lone pairs; H-O-H bond angle is about 104.5°.
• H2O2 (hydrogen peroxide): a non-planar, 'open-book' (skew) structure. The two oxygen atoms are joined by an O-O single bond, and each oxygen carries one H atom lying in a different plane; the O-O-H bonds are arranged with a dihedral angle of about 111° (in the gas phase).

PART (b)(ii) — Exchange reaction of deuterium: …