When the system takes heat from a hotter (hot) reservoir by an infinitesimal amount δ δ Q 1 ( ≥ ≥ 0 ), for the net change in entropy d S Total 1 to be positive or zero (i.e., non-negative) in this step (called the step 1 here) to fulfill the Second Law of Thermodynamics, the temperature of the hot reservoir T Hot needs to be equal to or greater than the temperature of the system at that instant; if the temperature of the system is given by T 1 at that instant, then d S Sys 1 = δ δ Q 1 T 1 as the entropy change in the system at the instant, and T Hot ≥ ≥ T 1 forces us to have: