Which law states that energy cannot be created or destroyed, only transformed?

• A. Second Law of Thermodynamics
• B. Third Law of Thermodynamics
• C. Zeroth Law of Thermodynamics
• D. First Law of Thermodynamics

Answer: (D)

Conservation of energy is the idea that energy cannot be created or destroyed in a closed system; it can only be transformed from one form to another. The First Law of Thermodynamics expresses this by saying that the change in a system’s internal energy equals the heat added to it plus the work done on it. In any process, energy may shift from chemical to kinetic, potential to thermal, electrical to light, and so on, but the total energy before and after remains the same. The other thermodynamics laws describe how systems reach equilibrium or relate to temperature and entropy, not the fundamental accounting of energy, so they don’t state this energy‑conservation idea as directly. So the statement that energy cannot be created or destroyed, only transformed, directly reflects the First Law.