O2 at low expense from AgIISO4: Silver(II) sulfate provides the first example among metal sulfates of low-temperature "reductive" thermal decomposition, which results in AgI disulfate and molecular dioxygen. Despite the similarity of this reaction to the one known for peroxodisulfates (e.g., K2S2O8), the thermodynamics and kinetics of both processes are markedly different, and when compared they severely disobey Hammond's rule (see scheme).