BIOC 212 Lecture Notes - Lecture 37: Equilibrium Constant, Thermal Energy, Gibbs Free Energy
29 May 2018
School
Department
Course
Professor
Thermodynamics & Equilibrium II
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First Law of Thermodynamics
• Energy can be converted from one form to another
o Cannot be created nor destroyed
• In biological systems, energy is stored and "managed" within chemical bonds
o Store energy as chemical bonds --can put them where want and control when
to use them
• Enthalpy: (H) is reflective of a measure of energy that can be released from
chemical bonds
o Or energy input required to break bond
o Negative enthalpy change spontaneously favors a reaction
Energy Conservation
• In biology, have continuous input of energy
o Most systems: come from sunlight
o Plants use solar energy and convert it into chemical bond energy through
photosynthesis
• CO2 + H2O --> sugars (carbon chains with O and H)
o Energetically unfavored; use sunlight to drive reaction
• Use cellular respiration to generate energy from chemical bonds
o Oxidation
• Complex network of interaction between ecology & biology
o Plants & sediments go into fossil fuels
o Burning releasing CO2 back to environment
o Things going back and forth, powered by solar energy
Gibbs Free Energy
• ∆G = ∆H - T∆S
o T: temperature in Kelvin
o Change in free energy is change in enthalpy - temperature x change in
entropy
o ∆H is energy released from chemical bonds (relates to first law)
o ∆S is measure of disorder (second law)
• A reaction will proceed in the direction that causes the change in free energy to
be less than zero
o ∆G < 0
o Go from something with higher to lower Gibb's energy; decrease
o Negative enthalpy change or positive entropy change (negative sign)
