Thermodynamics: Internal Energy, Its Laws and Heat-Engine Efficiency
How heat, work and the energy hidden inside matter obey a small set of powerful laws
Big Idea: Every body stores internal energy in the motion and arrangement of its molecules. You can change that energy in only two ways — by heating it or by doing work on it. Thermodynamics is the accounting system for this energy: the first law is strict energy bookkeeping, and the second law says heat has a preferred direction that limits how well any engine can turn heat into useful work.
By the end you will be able to:
- define internal energy and compute it for an ideal gas,
- calculate the work done by a gas as it expands,
- apply the first law of thermodynamics, ΔU = Q − A,
- state the second law and explain why no engine is 100% efficient,
- find the efficiency of a heat engine and the Carnot limit,
- describe how a refrigerator works and why engines matter for ecology.