When a certain compound is decomposed thermally, it means that the compound is separated into its individual pure elements occurring in nature. In this case, this happens in the presence of heat. The decomposition reaction is:
Whenever a force is applied to an object, causing the object to move, work is done by the force. ... Work can be either positive or negative: if the force has a component in the same direction as the displacement of the object, the force is doing positive work