Final answer:
When one mole of a liquid burns, it is generally an exothermic process where energy is released. However, during phase changes such as melting or evaporating, energy is absorbed without changing the temperature until the transition is complete.
Step-by-step explanation:
When one mole of a liquid burns, typically energy is released. This process, known as combustion, is an exothermic reaction because it liberates heat. Conversely, when a substance undergoes a phase change such as melting or evaporating, energy is absorbed to break the intermolecular forces holding the particles together, which is an endothermic process. However, during such phase changes, the temperature does not increase until the phase change is complete; for instance, the temperature of a mixture of ice and water remains at 0 °C until all the ice has melted. Conversely, during the reverse processes like freezing or condensation, energy is released as molecules come closer together to form a solid or liquid respectively.