Final answer:
Processes that result in a reduction of their potential energy are typically spontaneous processes. They are often characterized as exothermic, as they release energy to the surroundings. The correct term to complete the statement is 'spontaneous'.
Step-by-step explanation:
Processes that result in a reduction (lowering) of their potential energy tend to be spontaneous processes. When potential energy of a system decreases, it often indicates that energy is being released to the surroundings, a characteristic of an exothermic process. Therefore, the correct term to fill in the blank in the question is 'spontaneous'.
For example, when water vapor condenses to form liquid water, it is an exothermic process because heat is released. Similarly, when gasoline burns, it is also exothermic because energy is released in the form of heat and light. In contrast, an endothermic process is one in which a system absorbs heat from its surroundings, like when ice melts or when gold melts.
It is also noteworthy that although spontaneous processes may be reversible or irreversible, the question is emphasizing the energy aspect and not the reversibility or directionality of the process. An exothermic process will have negative enthalpy change, indicating the release of energy and a reduction in potential energy of the system.