Second Law of Thermodynamics

The Second Law of Thermodynamics introduces the concept of entropy and states that the total entropy of an isolated system always increases over time.

Mathematical Expressions

The change in entropy is defined as:

ΔS=QrevT\Delta S = \frac{Q_{rev}}{T}

For irreversible processes:

ΔStotal>0\Delta S_{total} > 0

Key Concepts

  • Entropy always increases in isolated systems
  • Heat flows spontaneously from hot to cold
  • Perfect heat engines are impossible
  • Carnot cycle and maximum efficiency

Heat Engine Efficiency

The maximum efficiency of a heat engine is given by:

η=1−TCTH\eta = 1 - \frac{T_C}{T_H}

Where:

  • TC = Cold reservoir temperature
  • TH = Hot reservoir temperature