Signs of Work in Thermodynamics: System vs Surroundings Explained | Positive vs negative work signs

Learn how to determine the signs of work in thermodynamics without memorizing random rules. In this General Chemistry lesson, we use a treadmill and moving walkway analogy to explain system vs surroundings, positive vs negative work, expansion vs compression, pressure-volume work, and the First Law of Thermodynamics. We’ll work through w = −PextΔV and ΔE = q + w step by step, including examples with expansion, compression, heat transfer, and changes in internal energy. By the end, you’ll understand why expansion gives negative work, compression gives positive work, and how to determine whether energy is entering or leaving the system. Topics include: System vs surroundings Positive and negative work Expansion vs compression Pressure-volume work w = −PextΔV ΔE = q + w Signs of q and w First Law of Thermodynamics Thermochemistry and General Chemistry practice