Let's examine each statement closely to identify the false one regarding an isothermal process:

Option A: System can exchange heat energy with the surrounding.

This statement is true. An isothermal process is one in which the temperature of the system remains constant. In order for the system to maintain constant temperature while performing work, there must be heat exchange with the surroundings.

Option B: Enthalpy of system remains constant.

This statement is false in general. Enthalpy, $$ H $$, is a state function defined by $$ H = U + PV $$, where $$ U $$ is the internal energy, $$ P $$ is the pressure, and $$ V $$ is the volume of the system. During an isothermal process, if the system does work or work is done on it (thus changing the volume in case the system is an ideal gas), then even if $$ U $$ remains constant (for an ideal gas), the product of $$ P \times V $$ may change because the pressure can change. Therefore, the enthalpy $$ H $$ can indeed change during an isothermal process, especially for a process in which the pressure and volume change.

Option C: Temperature of systems remains constant.

This statement is true. By definition, an isothermal process occurs at a constant temperature.

Option D: Internal energy of system remains constant.

This statement can be true or false depending on the nature of the gas. Specifically, for an ideal gas, the internal energy depends only on the temperature. Therefore, during an isothermal process for an ideal gas, where the temperature is constant, the internal energy also remains constant. However, for real gases or other systems, internal energy could be a function of other variables as well, potentially leading to changes even in an isothermal process.

Based on the above analysis, the false statement regarding an isothermal process is Option B: Enthalpy of the system remains constant, as enthalpy can change depending on the pressure-volume work done on or by the system.

Thermodynamics

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