🔍 Key Concepts

• Second Law of Thermodynamics and the natural direction of heat flow • Difference between hot and cold bodies in terms of energy • The idea of spontaneous vs. forced (refrigeration) heat transfer

💭 Think About

• Ask yourself: in everyday life, without any machines helping, which way does heat naturally move—toward hotter things or colder things? • Think about an ice cube in warm water: does the ice cube make the water colder, or does the water make the ice cube warmer—and which direction is the heat going? • Consider whether heat can naturally and continuously move both ways at the same time between hot and cold without outside work being done.

✅ Before You Answer

• Verify which option describes heat moving from hot to cold in a clear, one-way (uni-directional) manner under natural conditions • Eliminate any option that says heat naturally flows from cold to hot without work being applied (like in a refrigerator or heat pump) • Be careful with answers that suggest the direction of heat flow is unpredictable or bi-directional under normal, spontaneous conditions