Which law addresses the direction of heat flow in thermodynamic processes?

The correct choice is the Second Law of Thermodynamics, which fundamentally deals with the directionality of heat flow. According to this law, heat naturally flows from a hotter object to a colder object, not the other way around, in an isolated system. This directional flow is essential in understanding processes such as heat engines and refrigerators, where energy transfer is accompanied by a change in entropy, which measures the disorder within a system.

The Second Law underscores the concept that while energy can be transferred, it cannot be completely converted into work without some losses, leading to an increase in entropy. This principle is crucial in determining the feasibility of thermodynamic processes and in evaluating the efficiency of various energy systems.

The other laws—Zeroth, First, and Third—deal with different fundamental concepts in thermodynamics. The Zeroth Law establishes thermal equilibrium, the First Law is the principle of conservation of energy, and the Third Law gives insights into the behavior of systems at absolute zero. Each has its significance, but none address the specific directionality of heat transfer as the Second Law does.