Two large thermal reservoirs at constant absolute temperatures \(T_H\) and \(T_C\), where \(T_H > T_C\), are connected by a thermally conducting rod. Over a given time interval, an amount of thermal energy \(Q\) is transferred through the rod from the hotter reservoir to the colder reservoir without changing either reservoir's temperature. Which of the following expressions represents the total change in entropy \(\Delta S\) of the two-reservoir system?