[Nemesisof99]

Might sound simple but how do I actually determine whether a reaction is reversible or not simply by looking at the equation?
I've used the following ideas -
Precipitation reactions and exothermic reactions are generally irreversible. Like the reaction of metallic sodium with water.
But.. what about formation of potassium chloride and oxygen from potassium chlorate? How do I understand whether its reversible or not??