What is Thermodynamics?

Thermodynamics studies heat, work, temperature, and energy transfer. This guide explains the four laws of thermodynamics and their applications in engines, refrigerators, and natural systems.

The Four Laws of Thermodynamics

Zeroth Law

If two systems are in thermal equilibrium with a third, they're in equilibrium with each other. This defines temperature.

First Law

Energy cannot be created or destroyed, only converted. The change in internal energy equals heat added minus work done: ΔU = Q - W.

Second Law

Entropy always increases in isolated systems. Heat flows spontaneously from hot to cold. No process is 100% efficient.

Third Law

Entropy approaches zero as temperature approaches absolute zero. Perfect crystals have zero entropy at 0 K.

Applications

Thermodynamics powers engines, refrigerators, heat pumps, and explains weather patterns, chemical reactions, and the ultimate fate of the universe.