Since processes take place by chance alone, and this leads to increasing randomness, we can say that in any spontaneous process (one that takes place of its own accord and is not driven by outside influences) entropy increases. This is called the Second Law of Thermodynamics and is probably the most fundamental physical law. So processes that involve spreading out and increasing disorder are favoured over those where things become more ordered – students may have noticed this in their bedrooms!
The word feasible is also used to mean the same as spontaneous. The terms have nothing to do with the rate of a process. So a reaction may be feasible (spontaneous) but occur so slowly that in practice it does not occur at all. The reaction of diamond (pure carbon) with oxygen to form carbon dioxide is feasible (spontaneous) but we do not have to worry about jewellery burning in air at room temperature – ‘diamonds are forever’!.