• Living things require a continuous throughput of energy.
• With a knowledge of thermodynamics we can determine whether a physical process is possible.
• We want to know if a process will occur spontaneously.

  1. First Law of Thermodynamics: Energy Is Conserved

A. Energy

• Energy can neither be created or destroyed.
  
• DU = Ufinal - Uinitial = heatAbsorbedFrom - workDoneBy = q - w
• negative q is exothermic
• positive q is endothermic
• State Functions Are Independent of the Path a System Follows
• Experiments have demonstrated that the energy of a system depends only on its current state, not on how it reached that state.
• i.e. the universe prefers stateless transactions, cold hard cash, no ledger baby.
• i.e. the potential energy an anvil has is independent of the path that it took to get to that particular altitude.

B. Enthalpy

• Any combination of only state functions must also be a state function.
• Enthalpy is one such combination.
  
• H = U + PV
• Under constant pressure, a condition typical of most biochemical processes, the enthalpy change between the initial and final states of a process, DH, is the easily measured heat that it generates or absorbs.
• In general, the change of enthalpy in any hypothetical reaction pathway can be determined from the enthalpy change in any other reaction pathway between the same reactants and products.

  2. Second Law of Thermodynamics:
The Universe Tends Towards Maximum Disorder

A. Spontaneity and Disorder

• Spontaneous processes are characterized by the conversion of order (in this case the coherent motion of the swimmer's body) to chaos (the random thermal motion of water molecules)

B. Entropy

• S = kb ln W where
  S is the entropy
  kb is the Boltzmann constant 1.3807 x 10 -23 J/K
  W is the number of equivalent ways of arranging a system in a particular state.
• Entropy is a state function because it depends only on the parameters that describe a state.
• The laws of random chance cause any system of reasonable size to spontaneously adopt its most probable arrangement, the one in which entropy is a maximum, simply because this state is so overwhelmingly probable.
• For any constant energy process (DU=0)
  a spontaneous process is characterized by DS > 0.
• any spontaneous process must cause the entropy of the universe to increase
• the entropy of the universe tends towards a maximum
• a system can only be ordered at the expense of disordering its surroundings to an even greater extent by the application of energy to the system.
• When we eat, we gain energy by disordering the nutrients we consume.

   

B. Measurement of Entropy

• DS >= q/T
• The universe's entropy change in any real process is always greater than its ideal (reversible) value.

  3. Free Energy:
The Indicator of Spontaneity

A. Gibbs Free Energy: D G = DH - TDS

• DG <= 0 is the criterion of spontaneity we seek.
• DG < 0 is exergonic, they can be utilized to do work, they will happen
• DG > 0 is endogonic, they must be driven by the input of free energy

•  

B. Free Energy and Work

• DG for a biological process represents its maximum recoverable work.
• the work put into any system can never by fully recovered.
• an enzyme can only accelerate the attainment of thermodynamic equilibrium.
• it cannot promote a reaction that has a positive DG

  3. Chemical Equilibria

A. Equilibrium Constants

• The equilibrium constant of a reaction may therefore be calculated from standard free energy data and vice versa.
• Le Chatelier's principle states that, any deviation from equilibrium stimulates a process that tends to restore the system to equilibrium. All closed system must therefore reach equilibrium.

B. Standard Free Energy Changes

• Standard State Conventions In Biochemistry

C. Coupled Reactions

• The additivity of free energy changes allows an endergonic reaction to be driven by an exergonic reaction under the proper conditions.
• As long as the overall pathway is exergonic, it will operate in the forward direction.
• "Make sure the batteries are charged"