Waves that require an external heat source are classified as which type?

• A. Endothermic
• B. Exothermic
• C. Isothermal
• D. Exergonic

Answer: (A)

The main idea is that a process that needs heat from outside to proceed is endothermic. In endothermic events, energy is absorbed from the surroundings, so the system gains heat and the enthalpy change is positive. That matches the idea of requiring an external heat source to drive the waves or process forward.

If heat were released to the surroundings, the process would be exothermic, which is the opposite scenario. Isothermal describes maintaining a constant temperature, which isn’t the defining feature here—heat flow could occur, but the key point is whether heat enters the system. Exergonic describes energy release in terms of free energy, not specifically heat transfer. So the situation of needing external heat aligns with endothermic.