Final answer:
Catabolic reactions are exergonic because they release energy by breaking down molecules into smaller ones. These spontaneous reactions transfer energy to ATP and give off heat.
Step-by-step explanation:
Catabolic reactions are exothermic processes in organisms that break down molecules into smaller units and release energy. These reactions are usually spontaneous and are considered exergonic because they release more energy than is required to initiate the reaction. An example of a catabolic reaction is the breakdown of glucose during cellular respiration, which allows cells to harvest energy to carry out essential life processes.
Approximately 40 percent of the energy from catabolic reactions is transformed into adenosine triphosphate (ATP), which serves as the energy currency for cellular activities, while the remaining 60 percent is released as heat.