JAMB - Chemistry (2005 - No. 4)

The rusting of iron is a spontaneous reaction, meaning it occurs naturally without external energy input, as iron oxidizes to form rust (iron oxide) when exposed to oxygen and moisture. Although, it is a slow process, but there is an increase in entropy (ΔS) as well as the emission of heat which makes it a spontaneous reaction as the resulting change in Gibbs free energy will be negative.i.e ΔG = - ve