Which statement best describes the first law of thermodynamics?

• A. Energy can be created and destroyed but is mostly conserved.
• B. Energy cannot be created or destroyed but is always conserved.
• C. Energy exists only as heat.
• D. Energy is random and unpredictable.

Answer: (B)

Energy conservation is what the first law is about. It says energy can be moved around or changed from one form to another, but the total amount of energy in a closed system stays the same. That means you can transform electrical energy into light and thermal energy, or potential energy into kinetic energy, and so on, but you don’t create new energy or disappear energy into nothing. Heat and work are just ways energy can enter or leave a system, yet when you account for all forms of energy, the total remains constant. The other ideas miss this key point: energy isn’t confined to heat alone, it isn’t random and unpredictable in a fundamental sense, and energy isn’t created or destroyed—only transformed and transferred.