Closed System Thermodynamics
•1
st Law of Thermodynamics
– Irreversible processes result in spontaneous
conversion of internal energy to heat and
work
– At equilibrium a state of minimum internal
energy is attained
–Enthalpy
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Thermodynamics in Soil Science: Energy Flux, Entropy, and Soil Formation, Lecture notes of Thermodynamics
The principles of thermodynamics as applied to closed and open systems in the context of soil science. Topics include the 1st and 2nd laws of thermodynamics, energy sinks and sources, entropy, equilibrium versus steady state, and the pedogenic trajectory. The document also discusses methods for quantifying energy flux in soil systems using effective precipitation, biologic production, water balance, and timing of precipitation.
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2021/2022
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Closed System Thermodynamicsst^ • 1Law of Thermodynamics– Irreversible processes result in spontaneousconversion of internal energy to heat andwork– At equilibrium a state of minimum internalenergy is attained– Enthalpy
Closed System Thermodynamicsnd^ • 2Law of Thermodynamics– All isolated systems will spontaneouslyapproach a state of equilibrium– Entropy
Equilibrium versus Steady State• Closed systems – move towardsequilibrium – time invariant state withentropy maximization• Open systems – move towards steady-state and entropy minimization
Pedogenic Trajectory
- Rasmussen et al. (2005)Testing hypothesis that if soils are opensystems, one should be able to quantifysoil forming environment and soildevelopment based on energy flux into thesoil system
Energy Sink
Energy Source
Energy Flow
E ppt E npp
Soil System Ordering Processes• Humus Accumulation• Structure Formation• Horizonation• Illuviation – Eluviation• 2º Mineral Formation
Dissipative Processes• Respiration• Humus Decomposition• Mineral Weathering• Leaching• Erosion
) -1yr -2 (kJ m^ inE
(^) oC) (^) MAAT (
MAP (cm)
Jenny 1941 Idealized Model
Quantitative data fromWhite and Blum 1995
AridMollAnd
AlfEntIncept
UltSpod
10080604020 Energy Type Distribution (%)^0
EntAridMoll AlfAndIncept
UltSpod
(^350003000025000) )-1yr 20000 -2 (^15000) (kJ m inE 100005000 0
c b a
f e d h g