Enthalpy change during an isothermal process is not zero, as enthalpy depends on factors beyond temperature, including pressure and state of aggregation. While the internal energy change (dU) is zero for an ideal gas in an isothermal process, the enthalpy change (dH) can still be significant due to pressure-volume work. During phase transformations like vaporization or fusion, temperature remains constant, but enthalpy changes reflect the energy required to overcome intermolecular forces. Therefore, enthalpy values such as enthalpy of vaporization and fusion remain relevant despite constant temperature conditions. Understanding these concepts is crucial for analyzing thermodynamic processes.
