Heat, Energy, and Disorder
Thermodynamics governs heat, energy, and temperature in systems of many particles, bridging microscopic random motion to macroscopic properties via probability and statistics.
Temperature measures average particle kinetic energy (faster motion). Heat is energy transferred due to temperature differences, always flowing spontaneously from hot to cold.
| Property | Definition | Distinction |
|---|---|---|
| Temperature | Average particle kinetic energy | Intensive property (a level) |
| Heat | Energy in transit | Extensive energy (an amount) |
Common pitfall: Confusing heat with temperature. A large cool object can hold more total heat energy than a small hot one.
Laws and Statistical Entropy
The laws of thermodynamics dictate system behavior:
- First law: Energy is conserved: .
- Second law: Total entropy of an isolated system never decreases, .
- Third law: Entropy approaches a minimum near absolute zero.
Entropy measures disorder and the number of microstates. The second law is statistical: entropy tends to increase because disordered states are overwhelmingly more probable.
Common pitfall: Reading the second law as 'order is impossible.' Local order can form (like a fridge) as long as total entropy rises elsewhere. This statistical drift gives time its arrow and makes processes irreversible.