AS and A2 Chemistry notes and resources (WJEC specification) - UNIT CH5 Physical and inorganic chemistry

This unit develops ideas of redox, kinetics, energy changes and equilibria. The inorganic chemistry of some elements in various sections of the Periodic Table is studied.

19.2 - Entropy and feasibility of reactions

Candidates should be able to:

(f) appreciate that the entropy, S, of a chemical system is to a large degree determined by the freedom possessed by the molecules or atoms within the system, and that for all natural changes entropy increases towards a maximum (definitions not required);

(g) recognise that molecules or atoms in a solid have much more restricted freedom than in a gas and that, other factors being equal, entropy increases in the sequence S(solid) < S(liquid) < S(gas);

(h) apply the equation relating free energy change, G, to the entropy change, S, G = H . TS and understand that, for a reaction: if G is negative the reaction occurs spontaneously; if G is positive the reaction does not occur spontaneously; (i) understand that, because of the entropy change, endothermic processes such as the boiling of liquids, the solution of some salts and the thermal decomposition of oxysalts may still occur spontaneously.