H-theorem

Boltzmann's H-theorem states that the entropy of a closed system can only increase in the course of time, and must approach a limit as time tends to infinity.

$\sigma \geq 0$

where $\sigma$ is the entropy source strength, given by (Eq 36 Chap IX Ref. 2)

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sigma = -k \sum_{i,j} \int C(f_i,f_j) \ln f_i d {\mathbf u}_i}

where the function C() represents binary collisions. At equilibrium, Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sigma = 0} .

H-function

Boltzmann's H-function is defined by (Eq. 5.66 Ref. 3):

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle H=\iint f({\mathbf V}, {\mathbf r}, t) \ln f({\mathbf V}, {\mathbf r}, t) ~ d {\mathbf r} d{\mathbf V}}

where Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle {\mathbf V}} is the molecular velocity. A restatement of the H-theorem is

${\frac {dH}{dt}}\leq 0$

See also

• Boltzmann equation
• Second law of thermodynamics

References

1. L. Boltzmann "", Wiener Ber. 63 pp. 275- (1872)
2. Sybren R. De Groot and Peter Mazur "Non-Equilibrium Thermodynamics", Dover Publications
3. Robert Zwanzig "Nonequilibrium Statistical Mechanics", Oxford University Press (2001)